[PATCH] Fix tcp splice length

commit 6c242233648471868b44ea091d461f2db6a93f10
Author: Dimitris Michailidis [off-list ref]
Date:   Mon Jan 26 20:46:56 2009 -0800

    Fix length tcp_splice_data_recv passes to skb_splice_bits.
    
    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 [off-list ref]

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 0cd71b8..76b148b 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c

@@ -524,7 +524,8 @@ static int tcp_splice_data_recv(read_descriptor_t *rd_desc, struct sk_buff *skb,
 	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;

From: Dimitris Michailidis <redacted>
Date: Mon, 26 Jan 2009 21:12:21 -0800

    Fix length tcp_splice_data_recv passes to skb_splice_bits.

Eric, please review this.

CCed Willy Tarreau

Dimitris Michailidis a écrit :

Nice spot Dimitris !

Acked-by: Eric Dumazet <redacted>

This fixes a bug present in previous linux versions (before commit 
33966dd0e2f68f26943cd9ee93ec6abbc6547a8e tcp: splice as many packets
 as possible at once)
 
It should be backported as well, changing tss->len by min(tss->len, len) ?

From: Eric Dumazet <redacted>
Date: Tue, 27 Jan 2009 07:10:34 +0100

Nice spot Dimitris !

Acked-by: Eric Dumazet <redacted>

Ok, I'll apply this.

This fixes a bug present in previous linux versions (before commit 
33966dd0e2f68f26943cd9ee93ec6abbc6547a8e tcp: splice as many packets
 as possible at once)
 
It should be backported as well, changing tss->len by min(tss->len, len) ?

Indeed, I'll queue this up for -stable to remind myself about
this.

Thanks Eric.