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[73.241.150.58]) by smtp.gmail.com with ESMTPSA id a10sm17672568pfn.48.2021.08.31.12.38.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 31 Aug 2021 12:38:39 -0700 (PDT) Subject: Re: [PATCH net-next v3 RFC] skb_expand_head() adjust skb->truesize incorrectly To: Vasily Averin , Christoph Paasch , Eric Dumazet , "David S. Miller" Cc: Hideaki YOSHIFUJI , David Ahern , Jakub Kicinski , netdev , linux-kernel@vger.kernel.org, kernel@openvz.org, Julian Wiedmann , Alexey Kuznetsov References: <8fd56805-2ac8-dcbe-1337-b20f91f759d6@gmail.com> From: Eric Dumazet Message-ID: Date: Tue, 31 Aug 2021 12:38:38 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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 > Signed-off-by: Vasily Averin > --- > 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 >