skb_copy_and_csum_datagram_iovec doesn't check the actual length of the iovec's buffers to which it copies data, then memcpy_toiovec can copy to an address that was not specified by userspace, but garbage lying on the kernel stack. In some cases, this address can be a valid userspace address, to which memcpy_toiovec will write the buffers. This can happen when userspace calls write followed by recvmsg. In that case, memcpy_toiovec will dump the packet contents to the buffer passed to the write call, and can for example overwrite stack contents. Patch has been submitted: http://patchwork.ozlabs.org/patch/530642/ diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index ab3133797ff7..220454f32509 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -2431,7 +2431,7 @@ unsigned int datagram_poll(struct file *file, struct socket *sock, int skb_copy_datagram_iovec(const struct sk_buff *from, int offset, struct iovec *to, int size); int skb_copy_and_csum_datagram_iovec(struct sk_buff *skb, int hlen, - struct iovec *iov); + struct iovec *iov, int len); int skb_copy_datagram_from_iovec(struct sk_buff *skb, int offset, const struct iovec *from, int from_offset, int len); diff --git a/net/core/datagram.c b/net/core/datagram.c index 13bc7dad7990..3437762668af 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -796,6 +796,7 @@ EXPORT_SYMBOL(__skb_checksum_complete); * @skb: skbuff * @hlen: hardware length * @iov: io vector + * @len: amount of data to copy from skb to iov * * Caller _must_ check that skb will fit to this iovec. * @@ -805,11 +806,14 @@ EXPORT_SYMBOL(__skb_checksum_complete); * can be modified! */ int skb_copy_and_csum_datagram_iovec(struct sk_buff *skb, - int hlen, struct iovec *iov) + int hlen, struct iovec *iov, int len) { __wsum csum; int chunk = skb->len - hlen; + if (chunk > len) + chunk = len; + if (!chunk) return 0; diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 9fbd69efa999..cf6168b897c3 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -4934,7 +4934,7 @@ static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen) err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk); else err = skb_copy_and_csum_datagram_iovec(skb, hlen, - tp->ucopy.iov); + tp->ucopy.iov, chunk); if (!err) { tp->ucopy.len -= chunk; diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 6970e36ad7b8..8395cf5ec487 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1268,7 +1268,7 @@ try_again: else { err = skb_copy_and_csum_datagram_iovec(skb, sizeof(struct udphdr), - msg->msg_iov); + msg->msg_iov, copied); if (err == -EINVAL) goto csum_copy_err; diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c index 1f29996e368a..e6c9b4a7ee3c 100644 --- a/net/ipv6/raw.c +++ b/net/ipv6/raw.c @@ -492,7 +492,7 @@ static int rawv6_recvmsg(struct kiocb *iocb, struct sock *sk, goto csum_copy_err; err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, copied); } else { - err = skb_copy_and_csum_datagram_iovec(skb, 0, msg->msg_iov); + err = skb_copy_and_csum_datagram_iovec(skb, 0, msg->msg_iov, copied); if (err == -EINVAL) goto csum_copy_err; } diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c index 38625a91ec94..4011ccad6c9f 100644 --- a/net/ipv6/udp.c +++ b/net/ipv6/udp.c @@ -428,7 +428,8 @@ try_again: err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr), msg->msg_iov, copied); else { - err = skb_copy_and_csum_datagram_iovec(skb, sizeof(struct udphdr), msg->msg_iov); + err = skb_copy_and_csum_datagram_iovec(skb, sizeof(struct udphdr), + msg->msg_iov, copied); if (err == -EINVAL) goto csum_copy_err; } diff --git a/net/rxrpc/ar-recvmsg.c b/net/rxrpc/ar-recvmsg.c index 4949f753686c..83484ebf691d 100644 --- a/net/rxrpc/ar-recvmsg.c +++ b/net/rxrpc/ar-recvmsg.c @@ -186,7 +186,8 @@ int rxrpc_recvmsg(struct kiocb *iocb, struct socket *sock, msg->msg_iov, copy); } else { ret = skb_copy_and_csum_datagram_iovec(skb, offset, - msg->msg_iov); + msg->msg_iov, + copy); if (ret == -EINVAL) goto csum_copy_error; } Versions affected: stable kernels before v3.19 (3.x.y, x <= 18) that have backported commit 89c22d8c3b27 ("net: Fix skb csum races when peeking") v3.18.22 v3.14.54+ v3.12.48, v3.12.49 v3.10.90+ v3.2.72 3.16.7-ckt17, 3.16.7-ckt18 3.13.11-ckt27, 3.13.11-ckt28