[PATCH net-next v3 RFC] skb_expand_head() adjust skb->truesize incorrectly
From: Vasily Averin <hidden>
Date: 2021-08-31 14:34:35
Also in:
lkml
Subsystem:
networking [general], networking [sockets], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Kuniyuki Iwashima, Willem de Bruijn, Linus Torvalds
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 <redacted>
Signed-off-by: Vasily Averin <redacted>
---
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)))) { 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); + consume_skb(oskb); + } else if (sk) { + delta = osize - skb_end_offset(skb); + if (!is_skb_wmem(skb)) + skb_set_owner_w(skb, sk); + 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)); +} +EXPORT_SYMBOL(is_skb_wmem); + static bool can_skb_orphan_partial(const struct sk_buff *skb) { #ifdef CONFIG_TLS_DEVICE
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