From: Ilya Leoshkevich <iii@linux.ibm.com>

The kernel allows doing this, so let's allow this in qemu as well.
Valgrind relies on this.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20210601145600.3131040-2-iii@linux.ibm.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
---
 linux-user/signal.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/linux-user/signal.c b/linux-user/signal.c
index 0f19c59deee9..a8faea6f0909 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -853,7 +853,11 @@ int do_sigaction(int sig, const struct target_sigaction *act,
 
     trace_signal_do_sigaction_guest(sig, TARGET_NSIG);
 
-    if (sig < 1 || sig > TARGET_NSIG || sig == TARGET_SIGKILL || sig == TARGET_SIGSTOP) {
+    if (sig < 1 || sig > TARGET_NSIG) {
+        return -TARGET_EINVAL;
+    }
+
+    if (act && (sig == TARGET_SIGKILL || sig == TARGET_SIGSTOP)) {
         return -TARGET_EINVAL;
     }
 
-- 
2.31.1