[PATCH 3.16.y-ckt 56/58] net:socket: set msg_namelen to 0 if msg_name is passed as NULL in msghdr struct from userland.

[Luis Henriques]

3.16.7-ckt7 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ani Sinha <ani at arista.com>

commit 6a2a2b3ae0759843b22c929881cc184b00cc63ff upstream.

Linux manpage for recvmsg and sendmsg calls does not explicitly mention setting msg_namelen to 0 when
msg_name passed set as NULL. When developers don't set msg_namelen member in msghdr, it might contain garbage
value which will fail the validation check and sendmsg and recvmsg calls from kernel will return EINVAL. This will
break old binaries and any code for which there is no access to source code.
To fix this, we set msg_namelen to 0 when msg_name is passed as NULL from userland.

Signed-off-by: Ani Sinha <ani at arista.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Cc: Michal Marek <mmarek at suse.cz>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/socket.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/socket.c b/net/socket.c
index 7050240a951b..4980af97d87c 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1985,6 +1985,9 @@ static int copy_msghdr_from_user(struct msghdr *kmsg,
 	if (copy_from_user(kmsg, umsg, sizeof(struct msghdr)))
 		return -EFAULT;
 
+	if (kmsg->msg_name == NULL)
+		kmsg->msg_namelen = 0;
+
 	if (kmsg->msg_namelen < 0)
 		return -EINVAL;
 
-- 
2.1.4