[PATCH 4.14 42/44] seccomp: Invalidate seccomp mode to catch death failures

Greg Kroah-Hartman
2022-02-14T09:33:40Z

From: Kees Cook <keescook@chromium.org>

commit 495ac3069a6235bfdf516812a2a9b256671bbdf9 upstream.

If seccomp tries to kill a process, it should never see that process
again. To enforce this proactively, switch the mode to something
impossible. If encountered: WARN, reject all syscalls, and attempt to
kill the process again even harder.

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Fixes: 8112c4f140fa ("seccomp: remove 2-phase API")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/seccomp.c | 10 ++++++++++
1 file changed, 10 insertions(+)

--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -28,6 +28,9 @@
#include <linux/syscalls.h>
#include <linux/sysctl.h>

+/* Not exposed in headers: strictly internal use only. */
+#define SECCOMP_MODE_DEAD (SECCOMP_MODE_FILTER + 1)
+
#ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER
#include <asm/syscall.h>
#endif
@@ -632,6 +635,7 @@ static void __secure_computing_strict(in
#ifdef SECCOMP_DEBUG
dump_stack();
#endif
+ current->seccomp.mode = SECCOMP_MODE_DEAD;
seccomp_log(this_syscall, SIGKILL, SECCOMP_RET_KILL_THREAD, true);
do_exit(SIGKILL);
}
@@ -746,6 +750,7 @@ static int __seccomp_filter(int this_sys
case SECCOMP_RET_KILL_THREAD:
case SECCOMP_RET_KILL_PROCESS:
default:
+ current->seccomp.mode = SECCOMP_MODE_DEAD;
seccomp_log(this_syscall, SIGSYS, action, true);
/* Dump core only if this is the last remaining thread. */
if (action == SECCOMP_RET_KILL_PROCESS ||
@@ -798,6 +803,11 @@ int __secure_computing(const struct secc
return 0;
case SECCOMP_MODE_FILTER:
return __seccomp_filter(this_syscall, sd, false);
+ /* Surviving SECCOMP_RET_KILL_* must be proactively impossible. */
+ case SECCOMP_MODE_DEAD:
+ WARN_ON_ONCE(1);
+ do_exit(SIGKILL);
+ return -1;
default:
BUG();
}