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Subject[PATCH NET-NEXT] ipv6: skb_expand_head() adjust skb->truesize incorrectly
Date
Christoph Paasch reports [1] about incorrect skb->truesize
after skb_expand_head() call in ip6_xmit.
This happen because skb_set_owner_w() for newly clone skb is called
too early, before pskb_expand_head() where truesize is adjusted for
(!skb-sk) case.

[1] https://lkml.org/lkml/2021/8/20/1082

Reported-by: Christoph Paasch <christoph.paasch@gmail.com>
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
---
net/core/skbuff.c | 24 +++++++++++++-----------
1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index f931176..508d5c4 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1803,6 +1803,8 @@ struct sk_buff *skb_realloc_headroom(struct sk_buff *skb, unsigned int headroom)

struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom)
{
+ struct sk_buff *oskb = skb;
+ struct sk_buff *nskb = NULL;
int delta = headroom - skb_headroom(skb);

if (WARN_ONCE(delta <= 0,
@@ -1811,21 +1813,21 @@ struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom)

/* pskb_expand_head() might crash, if skb is shared */
if (skb_shared(skb)) {
- struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);
-
- if (likely(nskb)) {
- if (skb->sk)
- skb_set_owner_w(nskb, skb->sk);
- consume_skb(skb);
- } else {
- kfree_skb(skb);
- }
+ nskb = skb_clone(skb, GFP_ATOMIC);
skb = nskb;
}
if (skb &&
- pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) {
- kfree_skb(skb);
+ pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC))
skb = NULL;
+
+ if (!skb) {
+ kfree_skb(oskb);
+ if (nskb)
+ kfree_skb(nskb);
+ } else if (nskb) {
+ if (oskb->sk)
+ skb_set_owner_w(nskb, oskb->sk);
+ consume_skb(oskb);
}
return skb;
}
--
1.8.3.1
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