From b39e0213e5bee909cdfec569e071f5bc3060af12 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Mon, 7 Feb 2022 20:21:13 -0800 Subject: [PATCH] seccomp: Invalidate seccomp mode to catch death failures 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 Cc: Will Drewry Fixes: 8112c4f140fa ("seccomp: remove 2-phase API") Cc: stable@vger.kernel.org Signed-off-by: Kees Cook Signed-off-by: Greg Kroah-Hartman --- kernel/seccomp.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 4270ff81184d..158ae456e8b1 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -28,6 +28,9 @@ #include #include +/* Not exposed in headers: strictly internal use only. */ +#define SECCOMP_MODE_DEAD (SECCOMP_MODE_FILTER + 1) + #ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER #include #endif @@ -632,6 +635,7 @@ 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); } @@ -746,6 +750,7 @@ 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_PROCESS || @@ -798,6 +803,11 @@ 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(); }