[PATCH AUTOSEL 5.8 025/101] seccomp: kill process instead of thread for unknown actions

[Sasha Levin]

From: Rich Felker <dalias@xxxxxxxx>

[ Upstream commit 4d671d922d51907bc41f1f7f2dc737c928ae78fd ]

Asynchronous termination of a thread outside of the userspace thread
library's knowledge is an unsafe operation that leaves the process in
an inconsistent, corrupt, and possibly unrecoverable state. In order
to make new actions that may be added in the future safe on kernels
not aware of them, change the default action from
SECCOMP_RET_KILL_THREAD to SECCOMP_RET_KILL_PROCESS.

Signed-off-by: Rich Felker <dalias@xxxxxxxx>
Link: https://lore.kernel.org/r/20200829015609.GA32566@xxxxxxxxxxxxxxxxxxxxx
[kees: Fixed up coredump selection logic to match]
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/seccomp.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 54cf84bac3c9b..af1e43ddb9401 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -908,7 +908,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
 	default:
 		seccomp_log(this_syscall, SIGSYS, action, true);
 		/* Dump core only if this is the last remaining thread. */
-		if (action == SECCOMP_RET_KILL_PROCESS ||
+		if (action != SECCOMP_RET_KILL_THREAD ||
 		    get_nr_threads(current) == 1) {
 			kernel_siginfo_t info;
 
@@ -918,10 +918,10 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
 			seccomp_init_siginfo(&info, this_syscall, data);
 			do_coredump(&info);
 		}
-		if (action == SECCOMP_RET_KILL_PROCESS)
-			do_group_exit(SIGSYS);
-		else
+		if (action == SECCOMP_RET_KILL_THREAD)
 			do_exit(SIGSYS);
+		else
+			do_group_exit(SIGSYS);
 	}
 
 	unreachable();
-- 
2.25.1