From: Daniel Borkmann <dborkman@redhat.com>
Date: Mon, 30 Dec 2013 22:40:50 +0000 (+0100)
Subject: net: llc: fix use after free in llc_ui_recvmsg
X-Git-Tag: v3.2.55~67
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=10cc99961394c0e62e0742d5459f4b347f540d30;p=pandora-kernel.git

net: llc: fix use after free in llc_ui_recvmsg

[ Upstream commit 4d231b76eef6c4a6bd9c96769e191517765942cb ]

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@redhat.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c
index 99a60d545b24..f432d7b6d93a 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,
 	struct llc_sock *llc = llc_sk(sk);
 	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;
@@ -813,6 +813,7 @@ 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)
@@ -843,7 +844,7 @@ 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);