From: John Fastabend <john.fastabend@gmail.com>
To: Chengfeng Ye <nicoyip.dev@gmail.com>
Cc: Eric Dumazet <edumazet@google.com>,
Neal Cardwell <ncardwell@google.com>,
Kuniyuki Iwashima <kuniyu@google.com>,
Jakub Sitnicki <jakub@cloudflare.com>,
Jiayuan Chen <jiayuan.chen@linux.dev>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Paolo Abeni <pabeni@redhat.com>, Simon Horman <horms@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Alexei Starovoitov <ast@kernel.org>,
"open list:BPF [L7 FRAMEWORK] (sockmap)" <bpf@vger.kernel.org>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH] bpf, sockmap: Fix sk_redir use-after-free in send verdict
Date: Fri, 24 Jul 2026 16:06:03 -0700 [thread overview]
Message-ID: <amPvZHwUL5HlY0t0@john-p8> (raw)
In-Reply-To: <20260719152207.2892156-1-nicoyip.dev@gmail.com>
On Sun, Jul 19, 2026 at 11:22:07PM +0800, Chengfeng Ye wrote:
>sk_psock_msg_verdict() takes a socket reference for psock->sk_redir.
>tcp_bpf_send_verdict() copies that pointer while holding the source socket
>lock, but does not take a reference for the local copy before dropping the
>lock around tcp_bpf_sendmsg_redir().
>
>When apply_bytes keeps the cached verdict active, another sendmsg() on the
>same source socket can consume the remaining bytes and release the cached
>reference while the first thread still holds only the raw local pointer:
>
> CPU 0 CPU 1
> sk_redir = psock->sk_redir
> apply_bytes remains nonzero
> release_sock(sk)
> lock_sock(sk)
> apply_bytes reaches zero
> psock->sk_redir = NULL
> release_sock(sk)
> tcp_bpf_sendmsg_redir(sk_redir)
> sock_put(sk_redir)
> tcp_bpf_sendmsg_redir(sk_redir)
>
>The final sock_put() can free sk_redir before CPU 0 dereferences it.
>
>KASAN reported:
>
> BUG: KASAN: slab-use-after-free in tcp_bpf_sendmsg_redir+0xf39/0x1020
> Read of size 8 at addr ffff888108537090 by task poc/87
> Call Trace:
> tcp_bpf_sendmsg_redir+0xf39/0x1020
> tcp_bpf_sendmsg+0x977/0x1a50
> __sys_sendto+0x32c/0x3a0
> __x64_sys_sendto+0xdb/0x1b0
> Allocated by task 85:
> sk_prot_alloc+0x56/0x210
> sk_clone+0x6f/0x14b0
> inet_csk_clone_lock+0x24/0x740
> tcp_create_openreq_child+0x25/0x2710
> tcp_v4_syn_recv_sock+0x10a/0xe00
> Freed by task 0:
> __kasan_slab_free+0x43/0x70
> slab_free_after_rcu_debug+0xa6/0x1e0
> rcu_core+0x50a/0x1850
> Last potentially related work creation:
> __sk_destruct+0x3da/0x540
> sk_psock_destroy+0x81e/0xab0
> process_one_work+0x63a/0x1070
>
>Take a temporary socket reference while the source socket lock still
>protects psock->sk_redir, and drop it after tcp_bpf_sendmsg_redir()
>returns. This keeps each unlocked use independent of cached-verdict
>ownership.
>
>Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
>Cc: stable@vger.kernel.org
>Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
>---
Nice catch.
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
next prev parent reply other threads:[~2026-07-24 23:06 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-19 15:22 [PATCH] bpf, sockmap: Fix sk_redir use-after-free in send verdict Chengfeng Ye
2026-07-24 23:06 ` John Fastabend [this message]
2026-07-29 5:45 ` Emil Tsalapatis
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=amPvZHwUL5HlY0t0@john-p8 \
--to=john.fastabend@gmail.com \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=edumazet@google.com \
--cc=horms@kernel.org \
--cc=jakub@cloudflare.com \
--cc=jiayuan.chen@linux.dev \
--cc=kuba@kernel.org \
--cc=kuniyu@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=ncardwell@google.com \
--cc=netdev@vger.kernel.org \
--cc=nicoyip.dev@gmail.com \
--cc=pabeni@redhat.com \
--cc=stable@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox