This patch introduces the new argument [,elevateprivileges=allow|deny|children] to the `-sandbox on'. It allows or denies Qemu process to elevate its privileges by blacklisting all set*uid|gid system calls. The 'children' option will let forks and execves run unprivileged.
Signed-off-by: Eduardo Otubo <[email protected]> --- include/sysemu/seccomp.h | 1 + qemu-options.hx | 8 ++++++-- qemu-seccomp.c | 29 +++++++++++++++++++++++++++++ vl.c | 18 ++++++++++++++++++ 4 files changed, 54 insertions(+), 2 deletions(-) diff --git a/include/sysemu/seccomp.h b/include/sysemu/seccomp.h index 7a7bde246b..e6e78d85ce 100644 --- a/include/sysemu/seccomp.h +++ b/include/sysemu/seccomp.h @@ -16,6 +16,7 @@ #define QEMU_SECCOMP_H #define OBSOLETE 0x0001 +#define PRIVILEGED 0x0010 #include <seccomp.h> diff --git a/qemu-options.hx b/qemu-options.hx index c3200f303b..6dc776aae3 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -4004,8 +4004,10 @@ Old param mode (ARM only). ETEXI DEF("sandbox", HAS_ARG, QEMU_OPTION_sandbox, \ - "-sandbox on[,obsolete=allow] Enable seccomp mode 2 system call filter (default 'off').\n" \ - " obsolete: Allow obsolete system calls", + "-sandbox on[,obsolete=allow][,elevateprivileges=allow|deny|children]\n" \ + " Enable seccomp mode 2 system call filter (default 'off').\n" \ + " obsolete: Allow obsolete system calls\n" \ + " elevateprivileges: allows or denies Qemu process to elevate its privileges by blacklisting all set*uid|gid system calls. 'children' will deny set*uid|gid system calls for main Qemu process but will allow forks and execves to run unprivileged", QEMU_ARCH_ALL) STEXI @item -sandbox @var{arg}[,obsolete=@var{string}] @@ -4015,6 +4017,8 @@ disable it. The default is 'off'. @table @option @item obsolete=@var{string} Enable Obsolete system calls +@item elevateprivileges=@var{string} +Disable set*uid|gid systema calls @end table ETEXI diff --git a/qemu-seccomp.c b/qemu-seccomp.c index c6a8b28260..c204cef9ee 100644 --- a/qemu-seccomp.c +++ b/qemu-seccomp.c @@ -31,6 +31,19 @@ struct QemuSeccompSyscall { uint8_t priority; }; +static const struct QemuSeccompSyscall privileged_syscalls[] = { + { SCMP_SYS(setuid), 255 }, + { SCMP_SYS(setgid), 255 }, + { SCMP_SYS(setpgid), 255 }, + { SCMP_SYS(setsid), 255 }, + { SCMP_SYS(setreuid), 255 }, + { SCMP_SYS(setregid), 255 }, + { SCMP_SYS(setresuid), 255 }, + { SCMP_SYS(setresgid), 255 }, + { SCMP_SYS(setfsuid), 255 }, + { SCMP_SYS(setfsgid), 255 }, +}; + static const struct QemuSeccompSyscall obsolete[] = { { SCMP_SYS(readdir), 255 }, { SCMP_SYS(_sysctl), 255 }, @@ -110,6 +123,22 @@ int seccomp_start(uint8_t seccomp_opts) } } + if (seccomp_opts & PRIVILEGED) { + for (i = 0; i < ARRAY_SIZE(privileged_syscalls); i++) { + rc = seccomp_rule_add(ctx, SCMP_ACT_KILL, + privileged_syscalls[i].num, 0); + if (rc < 0) { + goto seccomp_return; + } + rc = seccomp_syscall_priority(ctx, privileged_syscalls[i].num, + privileged_syscalls[i].priority); + if (rc < 0) { + goto seccomp_return; + } + } + } + + rc = seccomp_load(ctx); seccomp_return: diff --git a/vl.c b/vl.c index 6a297851aa..0b857083a3 100644 --- a/vl.c +++ b/vl.c @@ -275,6 +275,10 @@ static QemuOptsList qemu_sandbox_opts = { .name = "obsolete", .type = QEMU_OPT_STRING, }, + { + .name = "elevateprivileges", + .type = QEMU_OPT_STRING, + }, { /* end of list */ } }, }; @@ -1046,6 +1050,20 @@ static int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp) } } + value = qemu_opt_get(opts,"elevateprivileges"); + if (value) { + if (strcmp(value, "deny") == 0) { + seccomp_opts |= PRIVILEGED; + } + if (strcmp(value, "children") == 0) { + seccomp_opts |= PRIVILEGED; + + /* calling prctl directly because we're + * not sure if host has CAP_SYS_ADMIN set*/ + prctl(PR_SET_NO_NEW_PRIVS, 1); + } + } + if (seccomp_start(seccomp_opts) < 0) { error_report("failed to install seccomp syscall filter " "in the kernel"); -- 2.13.0
