Commit 097b9146 authored by Marco Elver's avatar Marco Elver Committed by Jakub Kicinski

net: fix up truesize of cloned skb in skb_prepare_for_shift()

Avoid the assumption that ksize(kmalloc(S)) == ksize(kmalloc(S)): when
cloning an skb, save and restore truesize after pskb_expand_head(). This
can occur if the allocator decides to service an allocation of the same
size differently (e.g. use a different size class, or pass the
allocation on to KFENCE).

Because truesize is used for bookkeeping (such as sk_wmem_queued), a
modified truesize of a cloned skb may result in corrupt bookkeeping and
relevant warnings (such as in sk_stream_kill_queues()).

Link: https://lkml.kernel.org/r/X9JR/J6dMMOy1obu@elver.google.com
Reported-by: syzbot+7b99aafdcc2eedea6178@syzkaller.appspotmail.com
Suggested-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20210201160420.2826895-1-elver@google.comSigned-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent ec99a470
......@@ -3289,7 +3289,19 @@ EXPORT_SYMBOL(skb_split);
*/
static int skb_prepare_for_shift(struct sk_buff *skb)
{
return skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
int ret = 0;
if (skb_cloned(skb)) {
/* Save and restore truesize: pskb_expand_head() may reallocate
* memory where ksize(kmalloc(S)) != ksize(kmalloc(S)), but we
* cannot change truesize at this point.
*/
unsigned int save_truesize = skb->truesize;
ret = pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
skb->truesize = save_truesize;
}
return ret;
}
/**
......
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