[patch 36/47] tcp: Fix length tcp_splice_data_recv passes to skb_splice_bits.

[Greg KH <gregkh@suse.de>]

[-- Attachment #1: tcp-fix-length-tcp_splice_data_recv-passes-to-skb_splice_bits.patch --]
[-- Type: text/plain, Size: 1771 bytes --]

2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Dimitris Michailidis <dm@chelsio.com>

[ Upstream commit 9fa5fdf291c9b58b1cb8b4bb2a0ee57efa21d635 ]

tcp_splice_data_recv has two lengths to consider: the len parameter it
gets from tcp_read_sock, which specifies the amount of data in the skb,
and rd_desc->count, which is the amount of data the splice caller still
wants.  Currently it passes just the latter to skb_splice_bits, which then
splices min(rd_desc->count, skb->len - offset) bytes.

Most of the time this is fine, except when the skb contains urgent data.
In that case len goes only up to the urgent byte and is less than
skb->len - offset.  By ignoring len tcp_splice_data_recv may a) splice
data tcp_read_sock told it not to, b) return to tcp_read_sock a value > len.

Now, tcp_read_sock doesn't handle used > len and leaves the socket in a
bad state (both sk_receive_queue and copied_seq are bad at that point)
resulting in duplicated data and corruption.

Fix by passing min(rd_desc->count, len) to skb_splice_bits.

Signed-off-by: Dimitris Michailidis <dm@chelsio.com>
Acked-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 net/ipv4/tcp.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -520,7 +520,8 @@ static int tcp_splice_data_recv(read_des
 	struct tcp_splice_state *tss = rd_desc->arg.data;
 	int ret;
 
-	ret = skb_splice_bits(skb, offset, tss->pipe, rd_desc->count, tss->flags);
+	ret = skb_splice_bits(skb, offset, tss->pipe, min(rd_desc->count, len),
+			      tss->flags);
 	if (ret > 0)
 		rd_desc->count -= ret;
 	return ret;