From: Marco Elver <elver@xxxxxxxxxx> commit 097b9146c0e26aabaa6ff3e5ea536a53f5254a79 upstream. 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@xxxxxxxxxxxxxxxx Reported-by: syzbot+7b99aafdcc2eedea6178@xxxxxxxxxxxxxxxxxxxxxxxxx Suggested-by: Eric Dumazet <edumazet@xxxxxxxxxx> Signed-off-by: Marco Elver <elver@xxxxxxxxxx> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> Link: https://lore.kernel.org/r/20210201160420.2826895-1-elver@xxxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/core/skbuff.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -3089,7 +3089,19 @@ 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; } /**
