| Message ID | cd1ad476-2f2b-b3e5-4cae-442c91ad4279@virtuozzo.com (mailing list archive) |
|---|---|
| State | Deferred |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net,v6] skb_expand_head() adjust skb->truesize incorrectly | expand |
I've finally reproduced original issue by using reproducer from Christoph Paasch, and was able locally validate this patch. Thank you, Vasily Averin On 9/6/21 9:01 PM, 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 > > Fixes: f1260ff15a71 ("skbuff: introduce skb_expand_head()") > Fixes: 2d85a1b31dde ("ipv6: ip6_finish_output2: set sk into newly allocated nskb") > Reported-by: Christoph Paasch <christoph.paasch@gmail.com> > Signed-off-by: Vasily Averin <vvs@virtuozzo.com> > --- > v6: fixed delta, > improved comments > v5: fixed else condition, thanks to Eric > reworked update of expanded skb, > added corresponding comments > v4: decided to use is_skb_wmem() after pskb_expand_head() call > fixed 'return (EXPRESSION);' in os_skb_wmem according to Eric Dumazet > v3: removed __pskb_expand_head(), > added is_skb_wmem() helper for skb with wmem-compatible destructors > there are 2 ways to use it: > - before pskb_expand_head(), to create skb clones > - after successfull pskb_expand_head() to change owner on extended skb. > 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. > --- > include/net/sock.h | 1 + > net/core/skbuff.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++-------- > net/core/sock.c | 8 ++++++++ > 3 files changed, 60 insertions(+), 9 deletions(-) > > diff --git a/include/net/sock.h b/include/net/sock.h > index 95b2577..173d58c 100644 > --- a/include/net/sock.h > +++ b/include/net/sock.h > @@ -1695,6 +1695,7 @@ struct sk_buff *sock_wmalloc(struct sock *sk, unsigned long size, int force, > gfp_t priority); > void __sock_wfree(struct sk_buff *skb); > void sock_wfree(struct sk_buff *skb); > +bool is_skb_wmem(const struct sk_buff *skb); > struct sk_buff *sock_omalloc(struct sock *sk, unsigned long size, > gfp_t priority); > void skb_orphan_partial(struct sk_buff *skb); > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index f931176..e2a2aa31 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -1804,28 +1804,70 @@ 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); > + int osize = skb_end_offset(skb); > + struct sk_buff *oskb = NULL; > + struct sock *sk = skb->sk; > > if (WARN_ONCE(delta <= 0, > "%s is expecting an increase in the headroom", __func__)) > return skb; > > - /* pskb_expand_head() might crash, if skb is shared */ > + 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)) { > kfree_skb(skb); > - skb = NULL; > + kfree_skb(oskb); > + return NULL; > + } > + if (oskb) { > + if (sk) > + skb_set_owner_w(skb, sk); > + consume_skb(oskb); > + } else if (sk && skb->destructor != sock_edemux) { > + bool ref, set_owner; > + > + ref = false; set_owner = false; > + delta = skb_end_offset(skb) - osize; > + /* skb_set_owner_w() calls current skb destructor. > + * It can reduce sk_wmem_alloc to 0 and release sk, > + * To prevnt this, we increase sk_wmem_alloc in advance. > + * Some destructors might release the last sk_refcnt, > + * so it won't be possible to call sock_hold for !fullsock > + * We take an extra sk_refcnt to prevent this. > + * In any case we increase truesize of expanded skb. > + */ > + refcount_add(delta, &sk->sk_wmem_alloc); > + if (!is_skb_wmem(skb)) { > + set_owner = true; > + if (!sk_fullsock(sk) && IS_ENABLED(CONFIG_INET)) { > + /* skb_set_owner_w can set sock_edemux */ > + ref = refcount_inc_not_zero(&sk->sk_refcnt); > + if (!ref) { > + set_owner = false; > + WARN_ON(refcount_sub_and_test(delta, &sk->sk_wmem_alloc)); > + } > + } > + } > + if (set_owner) > + skb_set_owner_w(skb, sk); > +#ifdef CONFIG_INET > + if (skb->destructor == sock_edemux) { > + WARN_ON(refcount_sub_and_test(delta, &sk->sk_wmem_alloc)); > + if (ref) > + WARN_ON(refcount_dec_and_test(&sk->sk_refcnt)); > + } > +#endif > + skb->truesize += delta; > } > return skb; > } > diff --git a/net/core/sock.c b/net/core/sock.c > index 950f1e7..6cbda43 100644 > --- a/net/core/sock.c > +++ b/net/core/sock.c > @@ -2227,6 +2227,14 @@ void skb_set_owner_w(struct sk_buff *skb, struct sock *sk) > } > EXPORT_SYMBOL(skb_set_owner_w); > > +bool is_skb_wmem(const struct sk_buff *skb) > +{ > + return skb->destructor == sock_wfree || > + skb->destructor == __sock_wfree || > + (IS_ENABLED(CONFIG_INET) && skb->destructor == tcp_wfree); > +} > +EXPORT_SYMBOL(is_skb_wmem); > + > static bool can_skb_orphan_partial(const struct sk_buff *skb) > { > #ifdef CONFIG_TLS_DEVICE >
diff --git a/include/net/sock.h b/include/net/sock.h index 95b2577..173d58c 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1695,6 +1695,7 @@ struct sk_buff *sock_wmalloc(struct sock *sk, unsigned long size, int force, gfp_t priority); void __sock_wfree(struct sk_buff *skb); void sock_wfree(struct sk_buff *skb); +bool is_skb_wmem(const struct sk_buff *skb); struct sk_buff *sock_omalloc(struct sock *sk, unsigned long size, gfp_t priority); void skb_orphan_partial(struct sk_buff *skb); diff --git a/net/core/skbuff.c b/net/core/skbuff.c index f931176..e2a2aa31 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1804,28 +1804,70 @@ 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); + int osize = skb_end_offset(skb); + struct sk_buff *oskb = NULL; + struct sock *sk = skb->sk; if (WARN_ONCE(delta <= 0, "%s is expecting an increase in the headroom", __func__)) return skb; - /* pskb_expand_head() might crash, if skb is shared */ + 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)) { kfree_skb(skb); - skb = NULL; + kfree_skb(oskb); + return NULL; + } + if (oskb) { + if (sk) + skb_set_owner_w(skb, sk); + consume_skb(oskb); + } else if (sk && skb->destructor != sock_edemux) { + bool ref, set_owner; + + ref = false; set_owner = false; + delta = skb_end_offset(skb) - osize; + /* skb_set_owner_w() calls current skb destructor. + * It can reduce sk_wmem_alloc to 0 and release sk, + * To prevnt this, we increase sk_wmem_alloc in advance. + * Some destructors might release the last sk_refcnt, + * so it won't be possible to call sock_hold for !fullsock + * We take an extra sk_refcnt to prevent this. + * In any case we increase truesize of expanded skb. + */ + refcount_add(delta, &sk->sk_wmem_alloc); + if (!is_skb_wmem(skb)) { + set_owner = true; + if (!sk_fullsock(sk) && IS_ENABLED(CONFIG_INET)) { + /* skb_set_owner_w can set sock_edemux */ + ref = refcount_inc_not_zero(&sk->sk_refcnt); + if (!ref) { + set_owner = false; + WARN_ON(refcount_sub_and_test(delta, &sk->sk_wmem_alloc)); + } + } + } + if (set_owner) + skb_set_owner_w(skb, sk); +#ifdef CONFIG_INET + if (skb->destructor == sock_edemux) { + WARN_ON(refcount_sub_and_test(delta, &sk->sk_wmem_alloc)); + if (ref) + WARN_ON(refcount_dec_and_test(&sk->sk_refcnt)); + } +#endif + skb->truesize += delta; } return skb; } diff --git a/net/core/sock.c b/net/core/sock.c index 950f1e7..6cbda43 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -2227,6 +2227,14 @@ void skb_set_owner_w(struct sk_buff *skb, struct sock *sk) } EXPORT_SYMBOL(skb_set_owner_w); +bool is_skb_wmem(const struct sk_buff *skb) +{ + return skb->destructor == sock_wfree || + skb->destructor == __sock_wfree || + (IS_ENABLED(CONFIG_INET) && skb->destructor == tcp_wfree); +} +EXPORT_SYMBOL(is_skb_wmem); + static bool can_skb_orphan_partial(const struct sk_buff *skb) { #ifdef CONFIG_TLS_DEVICE
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 Fixes: f1260ff15a71 ("skbuff: introduce skb_expand_head()") Fixes: 2d85a1b31dde ("ipv6: ip6_finish_output2: set sk into newly allocated nskb") Reported-by: Christoph Paasch <christoph.paasch@gmail.com> Signed-off-by: Vasily Averin <vvs@virtuozzo.com> --- v6: fixed delta, improved comments v5: fixed else condition, thanks to Eric reworked update of expanded skb, added corresponding comments v4: decided to use is_skb_wmem() after pskb_expand_head() call fixed 'return (EXPRESSION);' in os_skb_wmem according to Eric Dumazet v3: removed __pskb_expand_head(), added is_skb_wmem() helper for skb with wmem-compatible destructors there are 2 ways to use it: - before pskb_expand_head(), to create skb clones - after successfull pskb_expand_head() to change owner on extended skb. 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. --- include/net/sock.h | 1 + net/core/skbuff.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++-------- net/core/sock.c | 8 ++++++++ 3 files changed, 60 insertions(+), 9 deletions(-)