[PATCH v2] skb_expand_head() adjust skb->truesize incorrectly
flat view
STALE1862d
From: Vasily Averin <hidden>
Date: 2021-08-29 13:00:08
Also in:
lkml
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
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> --- 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. --- net/core/skbuff.c | 43 +++++++++++++++++++++++++++++-------------- 1 file changed, 29 insertions(+), 14 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index f931176..4691023 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c@@ -1681,10 +1681,10 @@ struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb, int headroom, * reloaded after call to this function. */ -int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, - gfp_t gfp_mask) +static int __pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, + gfp_t gfp_mask, bool update_truesize) { - int i, osize = skb_end_offset(skb); + int delta, i, osize = skb_end_offset(skb); int size = osize + nhead + ntail; long off; u8 *data;
@@ -1756,9 +1756,13 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, * For the moment, we really care of rx path, or * when skb is orphaned (not attached to a socket). */ - if (!skb->sk || skb->destructor == sock_edemux) - skb->truesize += size - osize; - + delta = size - osize; + if (!skb->sk || skb->destructor == sock_edemux) { + skb->truesize += delta; + } else if (update_truesize) { + refcount_add(delta, &skb->sk->sk_wmem_alloc); + skb->truesize += delta; + } return 0; nofrags:
@@ -1766,6 +1770,12 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, nodata: return -ENOMEM; } + +int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, + gfp_t gfp_mask) +{ + return __pskb_expand_head(skb, nhead, ntail, gfp_mask, false); +} EXPORT_SYMBOL(pskb_expand_head); /* Make private copy of skb with writable head and some headroom */
@@ -1804,28 +1814,33 @@ 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); + struct sk_buff *oskb = NULL; 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)) { 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, true)) { kfree_skb(skb); - skb = NULL; + kfree_skb(oskb); + return NULL; + } + if (oskb) { + if (oskb->sk) + skb_set_owner_w(skb, oskb->sk); + consume_skb(oskb); } return skb; }
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1.8.3.1