seccomp: Only dump core when single-threaded

The SECCOMP_RET_KILL filter return code has always killed the current
thread, not the entire process. Changing this as a side-effect of dumping
core isn't a safe thing to do (a few test suites have already flagged this
behavioral change). Instead, restore the RET_KILL semantics, but still
dump core when a RET_KILL delivers SIGSYS to a single-threaded process.

Fixes: b25e67161c29 ("seccomp: dump core when using SECCOMP_RET_KILL")
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index f8f88ebcb3ba..e15185c28de5 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -643,11 +643,14 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
         default: {
                 siginfo_t info;
                 audit_seccomp(this_syscall, SIGSYS, action);
-                /* Show the original registers in the dump. */
-                syscall_rollback(current, task_pt_regs(current));
-                /* Trigger a manual coredump since do_exit skips it. */
-                seccomp_init_siginfo(&info, this_syscall, data);
-                do_coredump(&info);
+                /* Dump core only if this is the last remaining thread. */
+                if (get_nr_threads(current) == 1) {
+                        /* Show the original registers in the dump. */
+                        syscall_rollback(current, task_pt_regs(current));
+                        /* Trigger a manual coredump since do_exit skips it. */
+                        seccomp_init_siginfo(&info, this_syscall, data);
+                        do_coredump(&info);
+                }
                 do_exit(SIGSYS);
         }
         }