Messages in this thread | | | Subject | Re: [PATCH net-next v5] skb_expand_head() adjust skb->truesize incorrectly | From | Vasily Averin <> | Date | Thu, 2 Sep 2021 19:32:03 +0300 |
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On 9/2/21 6:53 PM, Christoph Paasch wrote: > On Thu, Sep 2, 2021 at 4:12 AM Vasily Averin <vvs@virtuozzo.com> 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()") >> Reported-by: Christoph Paasch <christoph.paasch@gmail.com> >> Signed-off-by: Vasily Averin <vvs@virtuozzo.com> >> --- >> 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 | 63 ++++++++++++++++++++++++++++++++++++++++++++++-------- >> net/core/sock.c | 8 +++++++ >> 3 files changed, 63 insertions(+), 9 deletions(-) > > Still the same issues around refcount as I reported in my other email. > > Did you try running the syzkaller reproducer on your setup?
no, I do not have
>> + } else if (sk && skb->destructor != sock_edemux) { >> + bool ref, set_owner; >> + >> + ref = false; set_owner = false; >> + delta = osize - skb_end_offset(skb);
error is here, should be instead delta = skb_end_offset(skb) - osize;
>> + /* skb_set_owner_w() calls current skb destructor. >> + * It can decrease sk_wmem_alloc to 0 and release sk, >> + * To prevnt it we increase sk_wmem_alloc earlier. >> + * Another kind of destructors can release last sk_refcnt, >> + * so it will be impossible to call sock_hold for !fullsock >> + * Take extra sk_refcnt to prevent it. >> + * Otherwise just 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 >> -- >> 1.8.3.1 >>
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