From: Vasily Averin vvs@virtuozzo.com
commit 54970a2fbb673f090b7f02d7f57b10b2e0707155 upstream.
syzbot reproduces BUG_ON in skb_checksum_help(): tun creates (bogus) skb with huge partial-checksummed area and small ip packet inside. Then ip_rcv trims the skb based on size of internal ip packet, after that csum offset points beyond of trimmed skb. Then checksum_tg() called via netfilter hook triggers BUG_ON:
offset = skb_checksum_start_offset(skb); BUG_ON(offset >= skb_headlen(skb));
To work around the problem this patch forces pskb_trim_rcsum_slow() to return -EINVAL in described scenario. It allows its callers to drop such kind of packets.
Link: https://syzkaller.appspot.com/bug?id=b419a5ca95062664fe1a60b764621eb4526e2cd... Reported-by: syzbot+7010af67ced6105e5ab6@syzkaller.appspotmail.com Signed-off-by: Vasily Averin vvs@virtuozzo.com Acked-by: Willem de Bruijn willemb@google.com Link: https://lore.kernel.org/r/1b2494af-2c56-8ee2-7bc0-923fcad1cdf8@virtuozzo.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/core/skbuff.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index b5d9c9b2c7028..5b87d2dd7151b 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1853,6 +1853,12 @@ int pskb_trim_rcsum_slow(struct sk_buff *skb, unsigned int len) skb->csum = csum_block_sub(skb->csum, skb_checksum(skb, len, delta, 0), len); + } else if (skb->ip_summed == CHECKSUM_PARTIAL) { + int hdlen = (len > skb_headlen(skb)) ? skb_headlen(skb) : len; + int offset = skb_checksum_start_offset(skb) + skb->csum_offset; + + if (offset + sizeof(__sum16) > hdlen) + return -EINVAL; } return __pskb_trim(skb, len); }