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seccomp: set the seccomp filter to all threads

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When using "-seccomp on", the seccomp policy is only applied to the
main thread, the vcpu worker thread and other worker threads created
after seccomp policy is applied; the seccomp policy is not applied to
e.g. the RCU thread because it is created before the seccomp policy is
applied and SECCOMP_FILTER_FLAG_TSYNC isn't used.

This can be verified with
for task in /proc/`pidof qemu`/task/*; do cat $task/status | grep Secc ; done
Seccomp:	2
Seccomp:	0
Seccomp:	0
Seccomp:	2
Seccomp:	2
Seccomp:	2

Starting with libseccomp 2.2.0 and kernel >= 3.17, we can use
seccomp_attr_set(ctx, > SCMP_FLTATR_CTL_TSYNC, 1) to update the policy
on all threads.

libseccomp requirement was bumped to 2.2.0 in previous patch.
libseccomp should fail to set the filter if it can't honour
SCMP_FLTATR_CTL_TSYNC (untested), and thus -sandbox will now fail on
kernel < 3.17.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Acked-by: Eduardo Otubo <otubo@redhat.com>
This commit is contained in:
Marc-André Lureau 2018-08-22 19:02:50 +02:00 committed by Eduardo Otubo
parent d0699bd37c
commit 70dfabeaa7
1 changed files with 5 additions and 0 deletions
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5
qemu-seccomp.c
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@ -149,6 +149,11 @@ static int seccomp_start(uint32_t seccomp_opts)
goto seccomp_return;
}
rc = seccomp_attr_set(ctx, SCMP_FLTATR_CTL_TSYNC, 1);
if (rc != 0) {
goto seccomp_return;
}
for (i = 0; i < ARRAY_SIZE(blacklist); i++) {
if (!(seccomp_opts & blacklist[i].set)) {
continue;