[PATCH 6.6 048/283] bpf, sockmap: Fix incorrect copied_seq calculation

Sasha Levin
2026-02-28T18:07:49Z

From: Jiayuan Chen <jiayuan.chen@linux.dev>

[ Upstream commit b40cc5adaa80e1471095a62d78233b611d7a558c ]

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 <jakub@cloudflare.com>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://lore.kernel.org/r/20260124113314.113584-2-jiayuan.chen@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/skmsg.h | 2 ++
net/core/skmsg.c | 27 ++++++++++++++++++++++++---
net/ipv4/tcp_bpf.c | 5 +++--
3 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index 32bbebf5b71e3..5c5a2d65184c3 100644
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -132,6 +132,8 @@ 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 6225547808a6b..9f522835bfafe 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -408,22 +408,26 @@ 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;
@@ -442,6 +446,9 @@ 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;
@@ -486,6 +493,13 @@ int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg,
out:
return copied;
}
+
+/* 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)
@@ -615,6 +629,12 @@ 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);
@@ -908,6 +928,7 @@ 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 7518d2af63088..5ff5faa2adde0 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;
--
2.51.0