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 @@ -628,6 +631,7 @@ 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); } @@ -742,6 +746,7 @@ 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 || @@ -794,6 +799,11 @@ 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(); }