[PATCH 3.14 131/140] net: gro: make sure skb->cb[] initial content has not to be zero

Greg Kroah-Hartman
2014-05-29T04:36:12Z

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3.14-stable review patch. If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 29e98242783ed3ba569797846a606ba66f781625 ]

Starting from linux-3.13, GRO attempts to build full size skbs.

Problem is the commit assumed one particular field in skb->cb[]
was clean, but it is not the case on some stacked devices.

Timo reported a crash in case traffic is decrypted before
reaching a GRE device.

Fix this by initializing NAPI_GRO_CB(skb)->last at the right place,
this also removes one conditional.

Thanks a lot to Timo for providing full reports and bisecting this.

Fixes: 8a29111c7ca6 ("net: gro: allow to build full sized skb")
Bisected-by: Timo Teras <timo.teras@iki.fi>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Timo Teräs <timo.teras@iki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/dev.c | 1 +
net/core/skbuff.c | 4 ++--
2 files changed, 3 insertions(+), 2 deletions(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3944,6 +3944,7 @@ static enum gro_result dev_gro_receive(s
}
NAPI_GRO_CB(skb)->count = 1;
NAPI_GRO_CB(skb)->age = jiffies;
+ NAPI_GRO_CB(skb)->last = skb;
skb_shinfo(skb)->gso_size = skb_gro_len(skb);
skb->next = napi->gro_list;
napi->gro_list = skb;
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3076,7 +3076,7 @@ int skb_gro_receive(struct sk_buff **hea
if (unlikely(p->len + len >= 65536))
return -E2BIG;

- lp = NAPI_GRO_CB(p)->last ?: p;
+ lp = NAPI_GRO_CB(p)->last;
pinfo = skb_shinfo(lp);

if (headlen <= offset) {
@@ -3192,7 +3192,7 @@ merge:

__skb_pull(skb, offset);

- if (!NAPI_GRO_CB(p)->last)
+ if (NAPI_GRO_CB(p)->last == p)
skb_shinfo(p)->frag_list = skb;
else
NAPI_GRO_CB(p)->last->next = skb;