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l2tp: Fix potential memory corruption in pppol2tp_recvmsg()

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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>
This commit is contained in:
James Chapman 2008-06-10 12:35:00 -07:00 committed by David S. Miller
parent 2e761e0532
commit 6b6707a50c
1 changed files with 12 additions and 8 deletions
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20
drivers/net/pppol2tp.c
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@ -783,14 +783,18 @@ static int pppol2tp_recvmsg(struct kiocb *iocb, struct socket *sock,
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;