[PATCH] signal: allow the null signal in rt_sigqueueinfo()

[Qian Cai]

Running the trinity fuzzer triggered this,

UBSAN: Undefined behaviour in kernel/signal.c:2946:7
shift exponent 4294967295 is too large for 64-bit type 'long unsigned
int'
[ 3752.406618]  dump_stack+0xe0/0x17a
[ 3752.419817]  ubsan_epilogue+0xd/0x4e
[ 3752.423429]  __ubsan_handle_shift_out_of_bounds+0x1d6/0x227
[ 3752.447269]  known_siginfo_layout.cold.9+0x16/0x1b
[ 3752.452105]  __copy_siginfo_from_user+0x4b/0x70
[ 3752.466620]  do_syscall_64+0x164/0x7ea
[ 3752.565030]  entry_SYSCALL_64_after_hwframe+0x49/0xbe

This is because signo is 0 from userspace, and then it ends up calling
(1UL << -1) in sig_specific_sicodes(). Since the null signal (0) is
allowed in the spec, just deal with it accordingly.

Signed-off-by: Qian Cai <cai@xxxxxx>
---
 kernel/signal.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index e1d7ad8e6ab1..970bb36837a9 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2943,7 +2943,7 @@ static bool known_siginfo_layout(unsigned sig, int si_code)
 	if (si_code == SI_KERNEL)
 		return true;
 	else if ((si_code > SI_USER)) {
-		if (sig_specific_sicodes(sig)) {
+		if (sig && sig_specific_sicodes(sig)) {
 			if (si_code <= sig_sicodes[sig].limit)
 				return true;
 		}
-- 
2.17.2 (Apple Git-113)