linux-kernel - [ 26/48] net:socket: set msg_namelen to 0 if msg_name is passed as NULL in msghdr struct from userland.

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Date:	Fri, 15 May 2015 10:05:56 +0200
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Ani Sinha <ani@...sta.com>,
	"David S. Miller" <davem@...emloft.net>,
	Ben Hutchings <ben@...adent.org.uk>, Willy Tarreau <w@....eu>
Subject: [ 26/48] net:socket: set msg_namelen to 0 if msg_name is passed
 as NULL in msghdr struct from userland.

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

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

From: Ani Sinha <ani@...sta.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@...sta.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
(cherry picked from commit d29f1f53e5299e0bbb3e33ef8d35ed657fa633b6)

Signed-off-by: Willy Tarreau <w@....eu>
---
 net/socket.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/socket.c b/net/socket.c
index 19671d8..a838a67 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1872,6 +1872,9 @@ 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;

-- 
1.7.12.2.21.g234cd45.dirty

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