From 6b6707a50c7598a83820077393f8823ab791abf8 Mon Sep 17 00:00:00 2001 From: James Chapman Date: Tue, 10 Jun 2008 12:35:00 -0700 Subject: [PATCH] l2tp: Fix potential memory corruption in pppol2tp_recvmsg() 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 Signed-off-by: James Chapman Signed-off-by: David S. Miller --- drivers/net/pppol2tp.c | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) diff --git a/drivers/net/pppol2tp.c b/drivers/net/pppol2tp.c index 70cfdb46aa27..f9298827a76c 100644 --- a/drivers/net/pppol2tp.c +++ b/drivers/net/pppol2tp.c @@ -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; -- 2.20.1