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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Neal Cardwell , Kuniyuki Iwashima , David Ahern , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Shuah Khan , Michal Luczaj , Cong Wang , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH bpf-next v7 1/3] bpf, sockmap: Fix incorrect copied_seq calculation In-Reply-To: <20260113025121.197535-2-jiayuan.chen@linux.dev> (Jiayuan Chen's message of "Tue, 13 Jan 2026 10:50:49 +0800") References: <20260113025121.197535-1-jiayuan.chen@linux.dev> <20260113025121.197535-2-jiayuan.chen@linux.dev> Date: Tue, 20 Jan 2026 16:01:21 +0100 Message-ID: <875x8wuy4e.fsf@cloudflare.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 On Tue, Jan 13, 2026 at 10:50 AM +08, Jiayuan Chen wrote: > A socket using sockmap has its own independent receive queue: ingress_msg. > This queue may contain data from its own protocol stack or from other > sockets. > > The issue is that when reading from ingress_msg, we update tp->copied_seq > by default. However, if the data is not from its own protocol stack, > tcp->rcv_nxt is not increased. Later, if we convert this socket to a > native socket, reading from this socket may fail because copied_seq might > be significantly larger than rcv_nxt. > > This fix also addresses the syzkaller-reported bug referenced in the > Closes tag. > > This patch marks the skmsg objects in ingress_msg. When reading, we update > copied_seq only if the data is from its own protocol stack. > > FD1:read() > -- FD1->copied_seq++ > | [read data] > | > [enqueue data] v > [sockmap] -> ingress to self -> ingress_msg queue > FD1 native stack ------> ^ > -- FD1->rcv_nxt++ -> redirect to other | [enqueue data] > | | > | ingress to FD1 > v ^ > ... | [sockmap] > FD2 native stack > > Closes: https://syzkaller.appspot.com/bug?extid=06dbd397158ec0ea4983 > Fixes: 04919bed948dc ("tcp: Introduce tcp_read_skb()") > Reviewed-by: Jakub Sitnicki > Signed-off-by: Jiayuan Chen > --- > include/linux/skmsg.h | 2 ++ > net/core/skmsg.c | 28 +++++++++++++++++++++++++--- > net/ipv4/tcp_bpf.c | 5 +++-- > 3 files changed, 30 insertions(+), 5 deletions(-) > > diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h > index 49847888c287..dfdc158ab88c 100644 > --- a/include/linux/skmsg.h > +++ b/include/linux/skmsg.h > @@ -141,6 +141,8 @@ int sk_msg_memcopy_from_iter(struct sock *sk, struct iov_iter *from, > struct sk_msg *msg, u32 bytes); > int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg, > int len, int flags); > +int __sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg, > + int len, int flags, int *copied_from_self); > bool sk_msg_is_readable(struct sock *sk); > > static inline void sk_msg_check_to_free(struct sk_msg *msg, u32 i, u32 bytes) > diff --git a/net/core/skmsg.c b/net/core/skmsg.c > index 2ac7731e1e0a..ca22ecdbf192 100644 > --- a/net/core/skmsg.c > +++ b/net/core/skmsg.c > @@ -409,22 +409,26 @@ int sk_msg_memcopy_from_iter(struct sock *sk, struct iov_iter *from, > } > EXPORT_SYMBOL_GPL(sk_msg_memcopy_from_iter); > > -/* Receive sk_msg from psock->ingress_msg to @msg. */ > -int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg, > - int len, int flags) > +int __sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg, > + int len, int flags, int *copied_from_self) > { > struct iov_iter *iter = &msg->msg_iter; > int peek = flags & MSG_PEEK; > struct sk_msg *msg_rx; > int i, copied = 0; > + bool from_self; > > msg_rx = sk_psock_peek_msg(psock); > + if (copied_from_self) > + *copied_from_self = 0; > + > while (copied != len) { > struct scatterlist *sge; > > if (unlikely(!msg_rx)) > break; > > + from_self = msg_rx->sk == sk; > i = msg_rx->sg.start; > do { > struct page *page; > @@ -443,6 +447,9 @@ int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg, > } > > copied += copy; > + if (from_self && copied_from_self) > + *copied_from_self += copy; > + > if (likely(!peek)) { > sge->offset += copy; > sge->length -= copy; > @@ -487,6 +494,14 @@ int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg, > out: > return copied; > } > +EXPORT_SYMBOL_GPL(__sk_msg_recvmsg); Nit: Sorry, I haven't caught that before. tcp_bpf is a built-in. We don't need to export this internal helper to modules. > + > +/* Receive sk_msg from psock->ingress_msg to @msg. */ > +int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg, > + int len, int flags) > +{ > + return __sk_msg_recvmsg(sk, psock, msg, len, flags, NULL); > +} > EXPORT_SYMBOL_GPL(sk_msg_recvmsg); > > bool sk_msg_is_readable(struct sock *sk) > @@ -616,6 +631,12 @@ static int sk_psock_skb_ingress_self(struct sk_psock *psock, struct sk_buff *skb > if (unlikely(!msg)) > return -EAGAIN; > skb_set_owner_r(skb, sk); > + > + /* This is used in tcp_bpf_recvmsg_parser() to determine whether the > + * data originates from the socket's own protocol stack. No need to > + * refcount sk because msg's lifetime is bound to sk via the ingress_msg. > + */ > + msg->sk = sk; > err = sk_psock_skb_ingress_enqueue(skb, off, len, psock, sk, msg, take_ref); > if (err < 0) > kfree(msg); > @@ -909,6 +930,7 @@ int sk_psock_msg_verdict(struct sock *sk, struct sk_psock *psock, > sk_msg_compute_data_pointers(msg); > msg->sk = sk; > ret = bpf_prog_run_pin_on_cpu(prog, msg); > + msg->sk = NULL; > ret = sk_psock_map_verd(ret, msg->sk_redir); > psock->apply_bytes = msg->apply_bytes; > if (ret == __SK_REDIRECT) { > diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c > index a268e1595b22..5c698fd7fbf8 100644 > --- a/net/ipv4/tcp_bpf.c > +++ b/net/ipv4/tcp_bpf.c > @@ -226,6 +226,7 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, > int peek = flags & MSG_PEEK; > struct sk_psock *psock; > struct tcp_sock *tcp; > + int copied_from_self = 0; > int copied = 0; > u32 seq; > > @@ -262,7 +263,7 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, > } > > msg_bytes_ready: > - copied = sk_msg_recvmsg(sk, psock, msg, len, flags); > + copied = __sk_msg_recvmsg(sk, psock, msg, len, flags, &copied_from_self); > /* The typical case for EFAULT is the socket was gracefully > * shutdown with a FIN pkt. So check here the other case is > * some error on copy_page_to_iter which would be unexpected. > @@ -277,7 +278,7 @@ static int tcp_bpf_recvmsg_parser(struct sock *sk, > goto out; > } > } > - seq += copied; > + seq += copied_from_self; > if (!copied) { > long timeo; > int data;