| Message ID | b66d9db6-f0ac-48a9-8062-49d6a5249d4b@virtuozzo.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next,v3,RFC] skb_expand_head() adjust skb->truesize incorrectly | expand |
On 8/31/21 7:34 AM, Vasily Averin wrote: > RFC because it have an extra changes: > new is_skb_wmem() helper can be called > - either before pskb_expand_head(), to create skb clones > for skb with destructors that does not change sk->sk_wmem_alloc > - or after pskb_expand_head(), to change owner in skb_set_owner_w() > > In current patch I've added both these ways, > we need to keep one of them. > --- > 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> > --- > 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 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 | 39 ++++++++++++++++++++++++++++----------- > net/core/sock.c | 8 ++++++++ > 3 files changed, 37 insertions(+), 11 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..3ce33f2 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -1804,30 +1804,47 @@ 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 */ > - if (skb_shared(skb)) { > + delta = SKB_DATA_ALIGN(delta); > + /* pskb_expand_head() might crash, if skb is shared. > + * Also we should clone skb if its destructor does > + * not adjust skb->truesize and sk->sk_wmem_alloc > + */ > + if (skb_shared(skb) || > + (sk && (!sk_fullsock(sk) || !is_skb_wmem(skb)))) { is_skb_wmem() is only possibly true for full sockets by definition. So the (sk_fullsock(sk) && is_skb_wmem(skb)) can be reduced to is_skb_wmem(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; > } > - return skb; > + if (oskb) { > + if (sk) > + skb_set_owner_w(skb, sk); Broken for non full sockets. Calling skb_set_owner_w(skb, sk) for them is a bug. > + consume_skb(oskb); > + } else if (sk) { > + delta = osize - skb_end_offset(skb); > + if (!is_skb_wmem(skb)) > + skb_set_owner_w(skb, sk); This would be broken for non full sockets. Calling skb_set_owner_w(skb, sk) for them is a bug. > + skb->truesize += delta; > + if (sk_fullsock(sk)) > + refcount_add(delta, &sk->sk_wmem_alloc); > + } return skb; > } > EXPORT_SYMBOL(skb_expand_head); > > diff --git a/net/core/sock.c b/net/core/sock.c > index 950f1e7..0315dcb 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)); No need for return (EXPRESSION); You can simply : return EXPRESSION; ie 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 >
On 8/31/21 10:38 PM, Eric Dumazet wrote: > On 8/31/21 7:34 AM, Vasily Averin wrote: >> RFC because it have an extra changes: >> new is_skb_wmem() helper can be called >> - either before pskb_expand_head(), to create skb clones >> for skb with destructors that does not change sk->sk_wmem_alloc >> - or after pskb_expand_head(), to change owner in skb_set_owner_w() >> >> In current patch I've added both these ways, >> we need to keep one of them. If nobody object I vote for 2nd way: >> diff --git a/net/core/skbuff.c b/net/core/skbuff.c >> index f931176..3ce33f2 100644 >> --- a/net/core/skbuff.c >> +++ b/net/core/skbuff.c >> @@ -1804,30 +1804,47 @@ 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) >> { ... skipped ... >> - return skb; >> + if (oskb) { >> + if (sk) >> + skb_set_owner_w(skb, sk); > > Broken for non full sockets. > Calling skb_set_owner_w(skb, sk) for them is a bug. I think you're wrong here. It is 100% equivalent of old code, skb_set_owner_w() handles sk_fullsock(sk) inside and does not adjust sk->sk_wmem_alloc. Please explain if I'm wrong. >> + consume_skb(oskb); >> + } else if (sk) { >> + delta = osize - skb_end_offset(skb); >> + if (!is_skb_wmem(skb)) >> + skb_set_owner_w(skb, sk); > > This would be broken for non full sockets. > Calling skb_set_owner_w(skb, sk) for them is a bug. See my comment above. >> + skb->truesize += delta; >> + if (sk_fullsock(sk)) >> + refcount_add(delta, &sk->sk_wmem_alloc); > > >> + } return skb; Strange line, will fix it. >> } >> EXPORT_SYMBOL(skb_expand_head);
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..3ce33f2 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1804,30 +1804,47 @@ 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 */ - if (skb_shared(skb)) { + delta = SKB_DATA_ALIGN(delta); + /* pskb_expand_head() might crash, if skb is shared. + * Also we should clone skb if its destructor does + * not adjust skb->truesize and sk->sk_wmem_alloc + */ + if (skb_shared(skb) || + (sk && (!sk_fullsock(sk) || !is_skb_wmem(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; } - return skb; + if (oskb) { + if (sk) + skb_set_owner_w(skb, sk); + consume_skb(oskb); + } else if (sk) { + delta = osize - skb_end_offset(skb); + if (!is_skb_wmem(skb)) + skb_set_owner_w(skb, sk); + skb->truesize += delta; + if (sk_fullsock(sk)) + refcount_add(delta, &sk->sk_wmem_alloc); + } return skb; } EXPORT_SYMBOL(skb_expand_head); diff --git a/net/core/sock.c b/net/core/sock.c index 950f1e7..0315dcb 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
RFC because it have an extra changes: new is_skb_wmem() helper can be called - either before pskb_expand_head(), to create skb clones for skb with destructors that does not change sk->sk_wmem_alloc - or after pskb_expand_head(), to change owner in skb_set_owner_w() In current patch I've added both these ways, we need to keep one of them. --- 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> --- 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 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 | 39 ++++++++++++++++++++++++++++----------- net/core/sock.c | 8 ++++++++ 3 files changed, 37 insertions(+), 11 deletions(-)