net: compat: Update get_compat_msghdr() to match copy_msghdr_from_user() behaviour

Commit db31c55a6fb2 (net: clamp ->msg_namelen instead of returning an
error) introduced the clamping of msg_namelen when the unsigned value
was larger than sizeof(struct sockaddr_storage). This caused a
msg_namelen of -1 to be valid. The native code was subsequently fixed by
commit dbb490b96584 (net: socket: error on a negative msg_namelen).

In addition, the native code sets msg_namelen to 0 when msg_name is
NULL. This was done in commit (6a2a2b3ae075 net:socket: set msg_namelen
to 0 if msg_name is passed as NULL in msghdr struct from userland) and
subsequently updated by 08adb7dabd48 (fold verify_iovec() into

This patch brings the get_compat_msghdr() in line with

Fixes: db31c55a6fb2 (net: clamp ->msg_namelen instead of returning an error)
Cc: David S. Miller <>
Cc: Dan Carpenter <>
Signed-off-by: Catalin Marinas <>
Signed-off-by: David S. Miller <>
(cherry picked from commit 91edd096e224941131f896b86838b1e59553696a)
Cc: Ben Hutchings <>
Signed-off-by: Willy Tarreau <>
Signed-off-by: Stefan Bader <>
diff --git a/net/compat.c b/net/compat.c
index a5848ac..8e39ff8 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -69,6 +69,13 @@
 	    __get_user(kmsg->msg_controllen, &umsg->msg_controllen) ||
 	    __get_user(kmsg->msg_flags, &umsg->msg_flags))
 		return -EFAULT;
+	if (!tmp1)
+		kmsg->msg_namelen = 0;
+	if (kmsg->msg_namelen < 0)
+		return -EINVAL;
 	if (kmsg->msg_namelen > sizeof(struct sockaddr_storage))
 		kmsg->msg_namelen = sizeof(struct sockaddr_storage);
 	kmsg->msg_name = compat_ptr(tmp1);