[PATCH] signal: strict valid signal check

[Hongchen Zhang]

The max usable signal number is limited by both _NSIG and task's
exit_code, and the max valid signal number encoded in task's
exit_code is 127. On the other hand _NSIG is normally power of 2,
so limit the rule in valid_signal to check a valid signal number.

Signed-off-by: Hongchen Zhang <zhanghongchen@xxxxxxxxxxx>
---
 include/linux/signal.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/signal.h b/include/linux/signal.h
index a6db6f2..9f1972e 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -270,7 +270,11 @@ static inline void init_sigpending(struct sigpending *sig)
 /* Test if 'sig' is valid signal. Use this instead of testing _NSIG directly */
 static inline int valid_signal(unsigned long sig)
 {
-	return sig <= _NSIG ? 1 : 0;
+	/* max usable signal number is limited by both _NSIG and task's
+	 * exit_code, and the max available signal number encoded in
+	 * task's exit_code is 127.
+	 */
+	return sig <= min(_NSIG, 127) ? 1 : 0;
 }
 
 struct timespec;
-- 
1.8.3.1