From: Marco Elver elver@google.com
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@elver.google.com Reported-by: syzbot+7b99aafdcc2eedea6178@syzkaller.appspotmail.com Suggested-by: Eric Dumazet edumazet@google.com Signed-off-by: Marco Elver elver@google.com Signed-off-by: Eric Dumazet edumazet@google.com Link: https://lore.kernel.org/r/20210201160420.2826895-1-elver@google.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/core/skbuff.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)
--- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -3285,7 +3285,19 @@ 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; }
/**