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Miller" , Jakub Kicinski , Paolo Abeni , Simon Horman , Daniel Borkmann , Alexei Starovoitov , "open list:BPF [L7 FRAMEWORK] (sockmap)" , 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 Message-ID: References: <20260719152207.2892156-1-nicoyip.dev@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline 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 >--- Nice catch. Reviewed-by: John Fastabend