linux-kernel - [PATCH 3.4 168/176] net:socket: set msg_namelen to 0 if msg_name is passed as NULL in msghdr struct from userland.

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Message-Id: <1428569224-23820-168-git-send-email-lizf@kernel.org>
Date:	Thu,  9 Apr 2015 16:46:56 +0800
From:	lizf@...nel.org
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Ani Sinha <ani@...sta.com>,
	"David S. Miller" <davem@...emloft.net>,
	Michal Marek <mmarek@...e.cz>, Zefan Li <lizefan@...wei.com>
Subject: [PATCH 3.4 168/176] net:socket: set msg_namelen to 0 if msg_name is passed as NULL in msghdr struct from userland.

From: Ani Sinha <ani@...sta.com>

3.4.107-rc1 review patch.  If anyone has any objections, please let me know.

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


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>
Cc: Michal Marek <mmarek@...e.cz>
Signed-off-by: Zefan Li <lizefan@...wei.com>
---
 net/socket.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/socket.c b/net/socket.c
index cc3fc4d..025f7f4 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1908,6 +1908,9 @@ 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;
 
-- 
1.9.1

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