[3.11.y.z extended stable] Patch "net: llc: fix use after free in llc_ui_recvmsg" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    net: llc: fix use after free in llc_ui_recvmsg

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 208227c81e0b1ab7352cfcf172d145288a3ea0c9 Mon Sep 17 00:00:00 2001
From: Daniel Borkmann <dborkman at redhat.com>
Date: Mon, 30 Dec 2013 23:40:50 +0100
Subject: net: llc: fix use after free in llc_ui_recvmsg

commit 4d231b76eef6c4a6bd9c96769e191517765942cb upstream.

While commit 30a584d944fb fixes datagram interface in LLC, a use
after free bug has been introduced for SOCK_STREAM sockets that do
not make use of MSG_PEEK.

The flow is as follow ...

  if (!(flags & MSG_PEEK)) {
    ...
    sk_eat_skb(sk, skb, false);
    ...
  }
  ...
  if (used + offset < skb->len)
    continue;

... where sk_eat_skb() calls __kfree_skb(). Therefore, cache
original length and work on skb_len to check partial reads.

Fixes: 30a584d944fb ("[LLX]: SOCK_DGRAM interface fixes")
Signed-off-by: Daniel Borkmann <dborkman at redhat.com>
Cc: Stephen Hemminger <stephen at networkplumber.org>
Cc: Arnaldo Carvalho de Melo <acme at ghostprotocols.net>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/llc/af_llc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c
index 8870988..c3ee805 100644
--- a/net/llc/af_llc.c
+++ b/net/llc/af_llc.c
@@ -715,7 +715,7 @@ static int llc_ui_recvmsg(struct kiocb *iocb, struct socket *sock,
 	unsigned long cpu_flags;
 	size_t copied = 0;
 	u32 peek_seq = 0;
-	u32 *seq;
+	u32 *seq, skb_len;
 	unsigned long used;
 	int target;	/* Read at least this many bytes */
 	long timeo;
@@ -812,6 +812,7 @@ static int llc_ui_recvmsg(struct kiocb *iocb, struct socket *sock,
 		}
 		continue;
 	found_ok_skb:
+		skb_len = skb->len;
 		/* Ok so how much can we use? */
 		used = skb->len - offset;
 		if (len < used)
@@ -844,7 +845,7 @@ static int llc_ui_recvmsg(struct kiocb *iocb, struct socket *sock,
 		}

 		/* Partial read */
-		if (used + offset < skb->len)
+		if (used + offset < skb_len)
 			continue;
 	} while (len > 0);

--
1.8.3.2