Re: [PATCH net v3] net: fix use-after-free when UDP GRO with shared fraglist

[Jakub Kicinski]

On Fri, 8 Jan 2021 11:18:39 +0100 Daniel Borkmann wrote:
> On 1/8/21 3:28 AM, Dongseok Yi wrote:
> > skbs in fraglist could be shared by a BPF filter loaded at TC. If TC
> > writes, it will call skb_ensure_writable -> pskb_expand_head to create
> > a private linear section for the head_skb. And then call
> > skb_clone_fraglist -> skb_get on each skb in the fraglist.
> > 
> > skb_segment_list overwrites part of the skb linear section of each
> > fragment itself. Even after skb_clone, the frag_skbs share their
> > linear section with their clone in PF_PACKET.
> > 
> > Both sk_receive_queue of PF_PACKET and PF_INET (or PF_INET6) can have
> > a link for the same frag_skbs chain. If a new skb (not frags) is
> > queued to one of the sk_receive_queue, multiple ptypes can see and
> > release this. It causes use-after-free.
> > 
> > [ 4443.426215] ------------[ cut here ]------------
> > [ 4443.426222] refcount_t: underflow; use-after-free.
> > [ 4443.426291] WARNING: CPU: 7 PID: 28161 at lib/refcount.c:190
> > refcount_dec_and_test_checked+0xa4/0xc8
> > [ 4443.426726] pstate: 60400005 (nZCv daif +PAN -UAO)
> > [ 4443.426732] pc : refcount_dec_and_test_checked+0xa4/0xc8
> > [ 4443.426737] lr : refcount_dec_and_test_checked+0xa0/0xc8
> > [ 4443.426808] Call trace:
> > [ 4443.426813]  refcount_dec_and_test_checked+0xa4/0xc8
> > [ 4443.426823]  skb_release_data+0x144/0x264
> > [ 4443.426828]  kfree_skb+0x58/0xc4
> > [ 4443.426832]  skb_queue_purge+0x64/0x9c
> > [ 4443.426844]  packet_set_ring+0x5f0/0x820
> > [ 4443.426849]  packet_setsockopt+0x5a4/0xcd0
> > [ 4443.426853]  __sys_setsockopt+0x188/0x278
> > [ 4443.426858]  __arm64_sys_setsockopt+0x28/0x38
> > [ 4443.426869]  el0_svc_common+0xf0/0x1d0
> > [ 4443.426873]  el0_svc_handler+0x74/0x98
> > [ 4443.426880]  el0_svc+0x8/0xc
> > 
> > Fixes: 3a1296a38d0c (net: Support GRO/GSO fraglist chaining.)
> > Signed-off-by: Dongseok Yi <dseok.yi@xxxxxxxxxxx>
> > Acked-by: Willem de Bruijn <willemb@xxxxxxxxxx>  
> 
> Acked-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>

Applied, thanks!