Re: [PATCH net-next v5] skb_expand_head() adjust skb->truesize incorrectly
flat view
From: Christoph Paasch <hidden>
Date: 2021-09-02 15:53:54
Also in:
lkml
On Thu, Sep 2, 2021 at 4:12 AM Vasily Averin [off-list ref] 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 <redacted> Signed-off-by: Vasily Averin <redacted> --- 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? Christoph
quoted hunk ↗ jump to hunk
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..29bb92e7 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c@@ -1804,28 +1804,73 @@ 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. + * Also we should clone skb if its destructor does + * not adjust skb->truesize and sk->sk_wmem_alloc + */ 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 = osize - skb_end_offset(skb); + /* 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