[PATCH 5.10 051/122] seccomp: Invalidate seccomp mode to catch death failures

Greg Kroah-Hartman
2024-02-27T14:27:47Z

From: Kees Cook <keescook@chromium.org>

[ Upstream commit 495ac3069a6235bfdf516812a2a9b256671bbdf9 ]

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: Sasha Levin <sashal@kernel.org>
---
kernel/seccomp.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 305f0eca163ed..0b0331346e4be 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -29,6 +29,9 @@
#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
@@ -795,6 +798,7 @@ static void __secure_computing_strict(int this_syscall)
#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);
}
@@ -1023,6 +1027,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
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_THREAD ||
@@ -1075,6 +1080,11 @@ int __secure_computing(const struct seccomp_data *sd)
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();
}
--
2.43.0