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Date:   Fri, 8 Jan 2021 11:18:39 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Dongseok Yi <dseok.yi@...sung.com>,
        "David S. Miller" <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Florian Westphal <fw@...len.de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Guillaume Nault <gnault@...hat.com>,
        Yunsheng Lin <linyunsheng@...wei.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Yadu Kishore <kyk.segfault@...il.com>,
        Marco Elver <elver@...gle.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, namkyu78.kim@...sung.com
Subject: Re: [PATCH net v3] net: fix use-after-free when UDP GRO with shared
 fraglist

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@...sung.com>
> Acked-by: Willem de Bruijn <willemb@...gle.com>

Acked-by: Daniel Borkmann <daniel@...earbox.net>

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