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[107.190.31.17]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-84ea03cbd1csm792779b3a.53.2026.07.28.22.45.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Jul 2026 22:45:45 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Wed, 29 Jul 2026 01:45:44 -0400 Message-Id: Cc: , , Subject: Re: [PATCH] bpf, sockmap: Fix sk_redir use-after-free in send verdict From: "Emil Tsalapatis" To: "Chengfeng Ye" , "Eric Dumazet" , "Neal Cardwell" , "Kuniyuki Iwashima" , "John Fastabend" , "Jakub Sitnicki" , "Jiayuan Chen" , "David S. Miller" , "Jakub Kicinski" , "Paolo Abeni" , "Simon Horman" , "Daniel Borkmann" , "Alexei Starovoitov" , "open list:BPF [L7 FRAMEWORK] (sockmap)" X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260719152207.2892156-1-nicoyip.dev@gmail.com> In-Reply-To: <20260719152207.2892156-1-nicoyip.dev@gmail.com> On Sun Jul 19, 2026 at 11:22 AM EDT, 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 socke= t > lock, but does not take a reference for the local copy before dropping th= e > lock around tcp_bpf_sendmsg_redir(). > > When apply_bytes keeps the cached verdict active, another sendmsg() on th= e > 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 =3D psock->sk_redir > apply_bytes remains nonzero > release_sock(sk) > lock_sock(sk) > apply_bytes reaches zero > psock->sk_redir =3D 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 Reviewed-by: Emil Tsalapatis > --- > net/ipv4/tcp_bpf.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c > index 8e905b50dead..69cc8bc33bcd 100644 > --- a/net/ipv4/tcp_bpf.c > +++ b/net/ipv4/tcp_bpf.c > @@ -469,6 +469,7 @@ static int tcp_bpf_send_verdict(struct sock *sk, stru= ct sk_psock *psock, > case __SK_REDIRECT: > redir_ingress =3D psock->redir_ingress; > sk_redir =3D psock->sk_redir; > + sock_hold(sk_redir); > sk_msg_apply_bytes(psock, tosend); > if (!psock->apply_bytes) { > /* Clean up before releasing the sock lock. */ > @@ -489,6 +490,7 @@ static int tcp_bpf_send_verdict(struct sock *sk, stru= ct sk_psock *psock, > =20 > if (eval =3D=3D __SK_REDIRECT) > sock_put(sk_redir); > + sock_put(sk_redir); > =20 > lock_sock(sk); > sk_mem_uncharge(sk, sent);