Patch "seccomp: Invalidate seccomp mode to catch death failures" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    seccomp: Invalidate seccomp mode to catch death failures

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     seccomp-invalidate-seccomp-mode-to-catch-death-failu.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ecf30932cf59a59ff4a6e5a91cc7a3daf513bea7
Author: Kees Cook <keescook@xxxxxxxxxxxx>
Date:   Mon Feb 7 20:21:13 2022 -0800

    seccomp: Invalidate seccomp mode to catch death failures
    
    [ 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@xxxxxxxxxxxxxx>
    Cc: Will Drewry <wad@xxxxxxxxxxxx>
    Fixes: 8112c4f140fa ("seccomp: remove 2-phase API")
    Cc: stable@xxxxxxxxxxxxxxx
    Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

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();
 	}