From: Vasily Averin <vvs@virtuozzo.com>
To: Christoph Paasch <christoph.paasch@gmail.com>,
Jakub Kicinski <kuba@kernel.org>,
Eric Dumazet <eric.dumazet@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
David Ahern <dsahern@kernel.org>, netdev <netdev@vger.kernel.org>,
linux-kernel@vger.kernel.org, kernel@openvz.org,
Julian Wiedmann <jwi@linux.ibm.com>
Subject: Re: [PATCH net v8] skb_expand_head() adjust skb->truesize incorrectly
Date: Tue, 21 Sep 2021 08:21:14 +0300 [thread overview]
Message-ID: <45b3cb13-8c6e-25a3-f568-921ab6f1ca8f@virtuozzo.com> (raw)
In-Reply-To: <be927ca4-6fd7-ce89-e472-bb1e5a0dc2a9@virtuozzo.com>
On 9/21/21 12:41 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
>
> 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>
> ---
> v8: clone non-wmem skb
> V7 (from kuba@):
> shift more magic into helpers,
> follow Eric's advice and don't inherit non-wmem skbs for now
> 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 | 33 +++++++++++++++++++++------------
> net/core/sock.c | 8 ++++++++
> 3 files changed, 30 insertions(+), 12 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..4b49f63 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -1804,30 +1804,39 @@ 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 sock *sk = skb->sk;
>
> 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)) {
> + if (skb_shared(skb) || !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 {
> - kfree_skb(skb);
> - }
> + if (unlikely(!nskb))
> + goto fail;
> +
> + if (sk)
> + skb_set_owner_w(nskb, sk);
> + consume_skb(skb);
> skb = nskb;
> }
> - if (skb &&
> - pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) {
> - kfree_skb(skb);
> - skb = NULL;
> + if (pskb_expand_head(skb, delta, 0, GFP_ATOMIC))
> + goto fail;
> +
> + if (sk) {
sock_edemux check is still required here too.
> + delta = skb_end_offset(skb) - osize;
> + refcount_add(delta, &sk->sk_wmem_alloc);
> + skb->truesize += delta;
> }
> return skb;
> +
> +fail:
> + kfree_skb(skb);
> + return NULL;
> }
> EXPORT_SYMBOL(skb_expand_head);
>
> 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
>
next prev parent reply other threads:[~2021-09-21 5:21 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20210920111259.18f9cc01@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
2021-09-20 21:41 ` [PATCH net v8] skb_expand_head() adjust skb->truesize incorrectly Vasily Averin
2021-09-21 5:21 ` Vasily Averin [this message]
2021-10-04 13:00 ` [PATCH net v9] " Vasily Averin
2021-10-04 13:14 ` Vasily Averin
2021-10-04 19:26 ` Eric Dumazet
2021-10-05 5:57 ` Vasily Averin
2021-10-20 16:14 ` Eric Dumazet
2021-10-20 16:18 ` Eric Dumazet
2021-10-22 10:28 ` [PATCH net v10] " Vasily Averin
2021-10-22 19:32 ` Eric Dumazet
2021-10-22 20:50 ` patchwork-bot+netdevbpf
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