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 --- kernel/seccomp.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 4d8f44a17727..db10e73d06e0 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 @@ -1010,6 +1013,7 @@ 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); } @@ -1261,6 +1265,7 @@ 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 || @@ -1309,6 +1314,11 @@ 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(); }