| From 54970a2fbb673f090b7f02d7f57b10b2e0707155 Mon Sep 17 00:00:00 2001 |
| From: Vasily Averin <vvs@virtuozzo.com> |
| Date: Mon, 14 Dec 2020 22:07:39 +0300 |
| Subject: net: drop bogus skb with CHECKSUM_PARTIAL and offset beyond end of trimmed packet |
| |
| 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=b419a5ca95062664fe1a60b764621eb4526e2cd0 |
| 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(+) |
| |
| --- a/net/core/skbuff.c |
| +++ b/net/core/skbuff.c |
| @@ -1592,6 +1592,12 @@ int pskb_trim_rcsum_slow(struct sk_buff |
| 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); |
| } |