ubsan: check panic_on_warn

Syzkaller expects kernel warnings to panic when the panic_on_warn sysctl
is set.  More work is needed here to have UBSan reuse the WARN
infrastructure, but for now, just check the flag manually.

Signed-off-by: Kees Cook <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Dan Carpenter <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Elena Petrova <[email protected]>
Cc: "Gustavo A. R. Silva" <[email protected]>
Link: https://lore.kernel.org/lkml/CACT4Y+bsLJ-wFx_TaXqax3JByUOWB3uk787LsyMVcfW6JzzGvg@mail.gmail.com
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

Author: kees

lib/ubsan.c

@@ -156,6 +156,17 @@ static void ubsan_epilogue(void)
 		"========================================\n");
 
 	current->in_ubsan--;
+
+	if (panic_on_warn) {
+		/*
+		 * This thread may hit another WARN() in the panic path.
+		 * Resetting this prevents additional WARN() from panicking the
+		 * system on this thread.  Other threads are blocked by the
+		 * panic_mutex in panic().
+		 */
+		panic_on_warn = 0;
+		panic("panic_on_warn set ...\n");
+	}
 }
 
 static void handle_overflow(struct overflow_data *data, void *lhs,