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Subject[patch 4/9] l2tp: Fix potential memory corruption in pppol2tp_recvmsg()
2.6.25-stable review patch.  If anyone has any objections, please let us
know.

------------------
From: James Chapman <jchapman@katalix.com>

[ Upstream commit 6b6707a50c7598a83820077393f8823ab791abf8 ]

This patch fixes a potential memory corruption in
pppol2tp_recvmsg(). If skb->len is bigger than the caller's buffer
length, memcpy_toiovec() will go into unintialized data on the kernel
heap, interpret it as an iovec and start modifying memory.

The fix is to change the memcpy_toiovec() call to
skb_copy_datagram_iovec() so that paged packets (rare for PPPOL2TP)
are handled properly. Also check that the caller's buffer is big
enough for the data and set the MSG_TRUNC flag if it is not so.

Reported-by: Ilja <ilja@netric.org>
Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/net/pppol2tp.c | 20 ++++++++++++--------
1 file changed, 12 insertions(+), 8 deletions(-)

--- a/drivers/net/pppol2tp.c
+++ b/drivers/net/pppol2tp.c
@@ -783,14 +783,18 @@ static int pppol2tp_recvmsg(struct kiocb
err = 0;
skb = skb_recv_datagram(sk, flags & ~MSG_DONTWAIT,
flags & MSG_DONTWAIT, &err);
- if (skb) {
- err = memcpy_toiovec(msg->msg_iov, (unsigned char *) skb->data,
- skb->len);
- if (err < 0)
- goto do_skb_free;
- err = skb->len;
- }
-do_skb_free:
+ if (!skb)
+ goto end;
+
+ if (len > skb->len)
+ len = skb->len;
+ else if (len < skb->len)
+ msg->msg_flags |= MSG_TRUNC;
+
+ err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, len);
+ if (likely(err == 0))
+ err = len;
+
kfree_skb(skb);
end:
return err;
--


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