FYI, John provided me a test kernel for 18.04 and it resolved the issue. This will be the basis of the SRU.
-- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1890848 Title: 'ptrace trace' needed to readlink() /proc/*/ns/* files on older kernels Status in linux package in Ubuntu: Fix Released Status in linux source package in Xenial: Triaged Status in linux source package in Bionic: Triaged Bug description: Per 'man namespaces': "Permission to dereference or read (readlink(2)) these symbolic links is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2)." This suggests that a 'ptrace read' rule should be sufficient to readlink() /proc/*/ns/*, which is the case with 5.4.0-42.46-generic (Ubuntu 20.04 LTS). However, on Ubuntu 18.04 LTS and 16.04 LTS, 'ptrace trace' is needed. Here is a reproducer: $ cat ./readlink-ns.c #include <errno.h> #include <linux/limits.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #include <unistd.h> void usage() { fprintf(stderr, "Usage: readlink-ns -p <pid> -n <ns>\n"); } int main(int argc, char *argv[]) { pid_t pid = 0; char *ns = NULL; char path[PATH_MAX] = {}; char rpath[PATH_MAX] = {}; int c; while ((c = getopt(argc, argv, "hn:p:")) != -1) { switch(c) { case 'n': ns = optarg; break; case 'p': pid = atoi(optarg); break; case 'h': usage(); return 0; case '?': usage(); return 1; default: return 1; } } int n = snprintf(path, sizeof(path), "/proc/%d/ns/%s", pid, ns); if (n < 0 || (size_t)n >= sizeof(path)) { fprintf(stderr, "cannot format string\n"); return 1; } path[n] = '\0'; printf("path: %s\n", path); n = readlink(path, rpath, sizeof(rpath)); if (n < 0) { perror("readlink()"); return 1; } else if (n == sizeof(rpath)) { fprintf(stderr, "cannot readlink()\n"); return 1; } printf("rpath: %s\n", rpath); return 0; } $ cat ./readlink-ns.apparmor #include <tunables/global> profile test { #include <abstractions/base> # focal ptrace (read) peer="unconfined", # xenial, bionic #ptrace (trace) peer="unconfined", } # bionic and xenial need 'ptrace trace' $ gcc ./readlink-ns.c && sudo apparmor_parser -r ./readlink-ns.apparmor && sudo aa-exec -p test -- ./a.out -p 1 -n pid path: /proc/1/ns/pid readlink(): Permission denied Denial: Aug 07 14:40:59 sec-bionic-amd64 kernel: audit: type=1400 audit(1596829259.675:872): apparmor="DENIED" operation="ptrace" profile="test" pid=1311 comm="a.out" requested_mask="trace" denied_mask="trace" peer="unconfined" # focal needs only 'ptrace read' $ gcc ./readlink-ns.c && sudo apparmor_parser -r ./readlink-ns.apparmor && sudo aa-exec -p test -- ./a.out -p 1 -n pid path: /proc/1/ns/pid rpath: pid:[4026531836] To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1890848/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
