[Qemu-devel] [PULL 1/2] seccomp: use SIGSYS signal instead of killing the thread

[Eduardo Otubo <otubo@redhat.com>]

From: Marc-André Lureau <marcandre.lureau@redhat.com>

The seccomp action SCMP_ACT_KILL results in immediate termination of
the thread that made the bad system call. However, qemu being
multi-threaded, it keeps running. There is no easy way for parent
process / management layer (libvirt) to know about that situation.

Instead, the default SIGSYS handler when invoked with SCMP_ACT_TRAP
will terminate the program and core dump.

This may not be the most secure solution, but probably better than
just killing the offending thread. SCMP_ACT_KILL_PROCESS has been
added in Linux 4.14 to improve the situation, which I propose to use
by default if available in the next patch.

Related to:
https://bugzilla.redhat.com/show_bug.cgi?id=1594456

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Acked-by: Eduardo Otubo <otubo@redhat.com>
---
 qemu-seccomp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/qemu-seccomp.c b/qemu-seccomp.c
index 9cd8eb9499..b117a92559 100644
--- a/qemu-seccomp.c
+++ b/qemu-seccomp.c
@@ -125,7 +125,7 @@ static int seccomp_start(uint32_t seccomp_opts)
             continue;
         }
 
-        rc = seccomp_rule_add_array(ctx, SCMP_ACT_KILL, blacklist[i].num,
+        rc = seccomp_rule_add_array(ctx, SCMP_ACT_TRAP, blacklist[i].num,
                                     blacklist[i].narg, blacklist[i].arg_cmp);
         if (rc < 0) {
             goto seccomp_return;
-- 
2.17.1