From 5c72263ef2fbe99596848f03758ae2dc593adf2c Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Tue, 8 Feb 2022 00:57:17 -0800 Subject: signal: HANDLER_EXIT should clear SIGNAL_UNKILLABLE MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Fatal SIGSYS signals (i.e. seccomp RET_KILL_* syscall filter actions) were not being delivered to ptraced pid namespace init processes. Make sure the SIGNAL_UNKILLABLE doesn't get set for these cases. Reported-by: Robert Święcki Suggested-by: "Eric W. Biederman" Fixes: 00b06da29cf9 ("signal: Add SA_IMMUTABLE to ensure forced siganls do not get changed") Cc: stable@vger.kernel.org Signed-off-by: Kees Cook Reviewed-by: "Eric W. Biederman" Link: https://lore.kernel.org/lkml/878rui8u4a.fsf@email.froward.int.ebiederm.org --- kernel/signal.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'kernel') diff --git a/kernel/signal.c b/kernel/signal.c index 38602738866e..9b04631acde8 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1342,9 +1342,10 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, } /* * Don't clear SIGNAL_UNKILLABLE for traced tasks, users won't expect - * debugging to leave init killable. + * debugging to leave init killable. But HANDLER_EXIT is always fatal. */ - if (action->sa.sa_handler == SIG_DFL && !t->ptrace) + if (action->sa.sa_handler == SIG_DFL && + (!t->ptrace || (handler == HANDLER_EXIT))) t->signal->flags &= ~SIGNAL_UNKILLABLE; ret = send_signal(sig, info, t, PIDTYPE_PID); spin_unlock_irqrestore(&t->sighand->siglock, flags); -- cgit v1.2.3 From 495ac3069a6235bfdf516812a2a9b256671bbdf9 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Mon, 7 Feb 2022 20:21:13 -0800 Subject: seccomp: Invalidate seccomp mode to catch death failures 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 --- kernel/seccomp.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'kernel') 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 #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 @@ -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(); } -- cgit v1.2.3