Re: KASAN: slab-use-after-free Read in ip_finish_output

On Wed, Mar 6, 2024 at 11:36 AM Florian Westphal [off-list ref] wrote:

Eric Dumazet [off-list ref] wrote:

quoted

On Wed, Mar 6, 2024 at 11:00 AM xingwei lee [off-list ref] wrote:

quoted

Hello, I found a new bug titled "KASAN: slab-use-after-free Read in
ip_finish_output” or “KASAN: slab-use-after-free in sk_to_full_sk" and
confirmed it in the latest net and net-next branch. After my simple
analysis, it may be related to the net/rose or AF_PACKET/PF_PACKET
socket.

I already had a syzbot report for this issue, thanks.

Adding Florian to the discussion.
The issue is cause by ip defrag layer, which calls skb_orphan()
These were my notes, I had little time to work on it so far.

quoted

Calling ip_defrag() in output path is also implying skb_orphan(),
which is buggy because output path relies on sk not disappearing.

Ugh.  Thanks for your annotations and notes, this is very helpful.

ipvlan (and two spots in ip_output.c do):

   err = ip_local_out(net, skb->sk, skb);

so skb->sk gets propagated down to __ip_finish_output(), long
after connrack defrag has called skb_orphan().

No idea yet how to fix it,

My plan was to refine "inet: frag: Always orphan skbs inside
ip_defrag()" and only do the skb_orphan()
for skb added to a frag_list.

The head skb would keep a reference to the socket.