Messages in this thread | | | Subject | Re: [PATCH v2] skb_expand_head() adjust skb->truesize incorrectly | From | Eric Dumazet <> | Date | Mon, 30 Aug 2021 09:01:01 -0700 |
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On 8/29/21 5:59 AM, Vasily Averin wrote: > Christoph Paasch reports [1] about incorrect skb->truesize > after skb_expand_head() call in ip6_xmit. > This may happen because of two reasons: > - skb_set_owner_w() for newly cloned skb is called too early, > before pskb_expand_head() where truesize is adjusted for (!skb-sk) case. > - pskb_expand_head() does not adjust truesize in (skb->sk) case. > In this case sk->sk_wmem_alloc should be adjusted too. > > [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> > --- > v2: based on patch version from Eric Dumazet, > added __pskb_expand_head() function, which can be forced > to adjust skb->truesize and sk->sk_wmem_alloc. > --- > net/core/skbuff.c | 43 +++++++++++++++++++++++++++++-------------- > 1 file changed, 29 insertions(+), 14 deletions(-) > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index f931176..4691023 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -1681,10 +1681,10 @@ struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb, int headroom, > * reloaded after call to this function. > */ > > -int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, > - gfp_t gfp_mask) > +static int __pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, > + gfp_t gfp_mask, bool update_truesize) > { > - int i, osize = skb_end_offset(skb); > + int delta, i, osize = skb_end_offset(skb); > int size = osize + nhead + ntail; > long off; > u8 *data; > @@ -1756,9 +1756,13 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, > * For the moment, we really care of rx path, or > * when skb is orphaned (not attached to a socket). > */ > - if (!skb->sk || skb->destructor == sock_edemux) > - skb->truesize += size - osize; > - > + delta = size - osize; > + if (!skb->sk || skb->destructor == sock_edemux) { > + skb->truesize += delta; > + } else if (update_truesize) {
Unfortunately we can not always do this sk_wmem_alloc change here.
Some skb have skb->sk set, but the 'reference on socket' is not through sk_wmem_alloc
It seems you need a helper to make sure skb->destructor is one of the destructors that use skb->truesize and sk->sk_wmem_alloc
For instance, skb_orphan_partial() could have been used.
> + refcount_add(delta, &skb->sk->sk_wmem_alloc); > + skb->truesize += delta; > + } > return 0; > > nofrags: > @@ -1766,6 +1770,12 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, > nodata: > return -ENOMEM; > } > + > +int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, > + gfp_t gfp_mask) > +{ > + return __pskb_expand_head(skb, nhead, ntail, gfp_mask, false); > +} > EXPORT_SYMBOL(pskb_expand_head); > > /* Make private copy of skb with writable head and some headroom */ > @@ -1804,28 +1814,33 @@ 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) > { > int delta = headroom - skb_headroom(skb); > + struct sk_buff *oskb = NULL; > > if (WARN_ONCE(delta <= 0, > "%s is expecting an increase in the headroom", __func__)) > return skb; > > + delta = SKB_DATA_ALIGN(delta); > /* 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 { > + if (unlikely(!nskb)) { > kfree_skb(skb); > + return NULL; > } > + oskb = skb; > skb = nskb; > } > - if (skb && > - pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) { > + if (__pskb_expand_head(skb, delta, 0, GFP_ATOMIC, true)) { > kfree_skb(skb); > - skb = NULL; > + kfree_skb(oskb); > + return NULL; > + } > + if (oskb) { > + if (oskb->sk) > + skb_set_owner_w(skb, oskb->sk); > + consume_skb(oskb); > } > return skb; > } >
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