From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.6 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 859EBC433EF for ; Mon, 6 Sep 2021 18:03:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5C9EC6101C for ; Mon, 6 Sep 2021 18:03:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244355AbhIFSEr (ORCPT ); Mon, 6 Sep 2021 14:04:47 -0400 Received: from relay.sw.ru ([185.231.240.75]:56336 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230219AbhIFSEo (ORCPT ); Mon, 6 Sep 2021 14:04:44 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=virtuozzo.com; s=relay; h=Content-Type:MIME-Version:Date:Message-ID:From: Subject; bh=dYP/kVnj128ydFQC67ehImb7kV/TltFY1+9Ktuzp6xA=; b=TnqDEF+bamo+Jgk4y qLXLFXXUUzHU3PUraXl11qn0eFHFfsIVeI44tA/lxa1C8JDABq+wcogaXlZuqIrzz3V/E3b4mzQZE cItqAJKpiRmFD4dQsTzSJnSOaKuesYr7Ey4lvVGJfkECxGDSDWILWqL/nAyVZ0gXZhdFyUkJsIybI =; Received: from [10.93.0.56] by relay.sw.ru with esmtp (Exim 4.94.2) (envelope-from ) id 1mNIxv-0013kX-Tv; Mon, 06 Sep 2021 21:03:31 +0300 Subject: Re: [PATCH net v6] skb_expand_head() adjust skb->truesize incorrectly From: Vasily Averin To: Christoph Paasch , Eric Dumazet , "David S. Miller" Cc: Hideaki YOSHIFUJI , David Ahern , Jakub Kicinski , netdev , linux-kernel@vger.kernel.org, kernel@openvz.org, Alexey Kuznetsov , Julian Wiedmann References: <63f90028-df26-d212-3bd2-65168736ce06@virtuozzo.com> Message-ID: <82b4794e-1e39-6ac8-1047-dd19350a168a@virtuozzo.com> Date: Mon, 6 Sep 2021 21:03:31 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 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: linux-kernel@vger.kernel.org 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 > Signed-off-by: Vasily Averin > --- > 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 >