Commit b160c285 authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

tcp: do not mess with cloned skbs in tcp_add_backlog() 



Heiner Kallweit reported that some skbs were sent with
the following invalid GSO properties :
- gso_size > 0
- gso_type == 0

This was triggerring a WARN_ON_ONCE() in rtl8169_tso_csum_v2.

Juerg Haefliger was able to reproduce a similar issue using
a lan78xx NIC and a workload mixing TCP incoming traffic
and forwarded packets.

The problem is that tcp_add_backlog() is writing
over gso_segs and gso_size even if the incoming packet will not
be coalesced to the backlog tail packet.

While skb_try_coalesce() would bail out if tail packet is cloned,
this overwriting would lead to corruptions of other packets
cooked by lan78xx, sharing a common super-packet.

The strategy used by lan78xx is to use a big skb, and split
it into all received packets using skb_clone() to avoid copies.
The drawback of this strategy is that all the small skb share a common
struct skb_shared_info.

This patch rewrites TCP gso_size/gso_segs handling to only
happen on the tail skb, since skb_try_coalesce() made sure
it was not cloned.

Fixes: 4f693b55 ("tcp: implement coalescing on backlog queue")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Bisected-by: default avatarJuerg Haefliger <juergh@canonical.com>
Tested-by: default avatarJuerg Haefliger <juergh@canonical.com>
Reported-by: default avatarHeiner Kallweit <hkallweit1@gmail.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=209423
Link: https://lore.kernel.org/r/20210119164900.766957-1-eric.dumazet@gmail.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent fd23d2dc

net/ipv4/tcp_ipv4.c

+13 −12
Original line number Diff line number Diff line
@@ -1760,6 +1760,7 @@ int tcp_v4_early_demux(struct sk_buff *skb) 
bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb)

{

	u32 limit = READ_ONCE(sk->sk_rcvbuf) + READ_ONCE(sk->sk_sndbuf);

	u32 tail_gso_size, tail_gso_segs;

	struct skb_shared_info *shinfo;

	const struct tcphdr *th;

	struct tcphdr *thtail;
@@ -1767,6 +1768,7 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb) 
	unsigned int hdrlen;

	bool fragstolen;

	u32 gso_segs;

	u32 gso_size;

	int delta;



	/* In case all data was pulled from skb frags (in __pskb_pull_tail()),
@@ -1792,13 +1794,6 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb) 
	 */

	th = (const struct tcphdr *)skb->data;

	hdrlen = th->doff * 4;

	shinfo = skb_shinfo(skb);



	if (!shinfo->gso_size)

		shinfo->gso_size = skb->len - hdrlen;



	if (!shinfo->gso_segs)

		shinfo->gso_segs = 1;



	tail = sk->sk_backlog.tail;

	if (!tail)
@@ -1821,6 +1816,15 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb) 
		goto no_coalesce;



	__skb_pull(skb, hdrlen);



	shinfo = skb_shinfo(skb);

	gso_size = shinfo->gso_size ?: skb->len;

	gso_segs = shinfo->gso_segs ?: 1;



	shinfo = skb_shinfo(tail);

	tail_gso_size = shinfo->gso_size ?: (tail->len - hdrlen);

	tail_gso_segs = shinfo->gso_segs ?: 1;



	if (skb_try_coalesce(tail, skb, &fragstolen, &delta)) {

		TCP_SKB_CB(tail)->end_seq = TCP_SKB_CB(skb)->end_seq;
@@ -1847,11 +1851,8 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb) 
		}



		/* Not as strict as GRO. We only need to carry mss max value */

		skb_shinfo(tail)->gso_size = max(shinfo->gso_size,

						 skb_shinfo(tail)->gso_size);



		gso_segs = skb_shinfo(tail)->gso_segs + shinfo->gso_segs;

		skb_shinfo(tail)->gso_segs = min_t(u32, gso_segs, 0xFFFF);

		shinfo->gso_size = max(gso_size, tail_gso_size);

		shinfo->gso_segs = min_t(u32, gso_segs + tail_gso_segs, 0xFFFF);



		sk->sk_backlog.len += delta;

		__NET_INC_STATS(sock_net(sk),