[PATCH bpf v3 0/2] bpf: Reject TCP_NODELAY in TCP header option callbacks

[PATCH bpf v3 0/2] bpf: Reject TCP_NODELAY in TCP header option callbacks

[KaFai Wan]

This small patchset is about avoid infinite recursion in TCP header option
callbacks via TCP_NODELAY setsockopt.

v3:
 - Remove CONFIG_INET check and add comment (Martin and Jiayuan)
 - Fix the test case (Martin)

v2:
 - Reject TCP_NODELAY in bpf_sock_ops_setsockopt() (AI and Martin)
 https://lore.kernel.org/bpf/20260416112308.1820332-1-kafai.wan@linux.dev/

v1:
 https://lore.kernel.org/bpf/20260414112310.1285783-1-kafai.wan@linux.dev/

---
KaFai Wan (2):
  bpf: Reject TCP_NODELAY in TCP header option callbacks
  selftests/bpf: Test TCP_NODELAY in TCP hdr opt callbacks

 net/core/filter.c                                 |  6 ++++++
 .../selftests/bpf/prog_tests/tcp_hdr_options.c    | 12 +++++++++++-
 .../bpf/progs/test_misc_tcp_hdr_options.c         | 15 ++++++++++++++-
 3 files changed, 31 insertions(+), 2 deletions(-)

-- 
2.43.0

[PATCH bpf v3 1/2] bpf: Reject TCP_NODELAY in TCP header option callbacks

[KaFai Wan]

A BPF_SOCK_OPS program can enable
BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG and then call
bpf_setsockopt(TCP_NODELAY) from BPF_SOCK_OPS_HDR_OPT_LEN_CB or
BPF_SOCK_OPS_WRITE_HDR_OPT_CB.

In these callbacks, bpf_setsockopt(TCP_NODELAY) can reach
__tcp_sock_set_nodelay(), which can call tcp_push_pending_frames().

From BPF_SOCK_OPS_HDR_OPT_LEN_CB, tcp_push_pending_frames() can call
tcp_current_mss(), which calls tcp_established_options() and re-enters
bpf_skops_hdr_opt_len().

BPF_SOCK_OPS_HDR_OPT_LEN_CB
  -> bpf_setsockopt(TCP_NODELAY)
    -> tcp_push_pending_frames()
      -> tcp_current_mss()
        -> tcp_established_options()
          -> bpf_skops_hdr_opt_len()
            -> BPF_SOCK_OPS_HDR_OPT_LEN_CB

From BPF_SOCK_OPS_WRITE_HDR_OPT_CB, tcp_push_pending_frames() can call
tcp_write_xmit(), which calls tcp_transmit_skb().  That path recomputes
header option length through tcp_established_options() and
bpf_skops_hdr_opt_len() before re-entering bpf_skops_write_hdr_opt().

BPF_SOCK_OPS_WRITE_HDR_OPT_CB
  -> bpf_setsockopt(TCP_NODELAY)
    -> tcp_push_pending_frames()
      -> tcp_write_xmit()
        -> tcp_transmit_skb()
          -> tcp_established_options()
            -> bpf_skops_hdr_opt_len()
          -> bpf_skops_write_hdr_opt()
            -> BPF_SOCK_OPS_WRITE_HDR_OPT_CB

This leads to unbounded recursion and can overflow the kernel stack.

Reject TCP_NODELAY with -EOPNOTSUPP in bpf_sock_ops_setsockopt()
when bpf_setsockopt() is called from
BPF_SOCK_OPS_HDR_OPT_LEN_CB or BPF_SOCK_OPS_WRITE_HDR_OPT_CB.

Reported-by: Quan Sun <2022090917019@std.uestc.edu.cn>
Reported-by: Yinhao Hu <dddddd@hust.edu.cn>
Reported-by: Kaiyan Mei <M202472210@hust.edu.cn>
Closes: https://lore.kernel.org/bpf/d1d523c9-6901-4454-a183-94462b8f3e4e@std.uestc.edu.cn/
Fixes: 7e41df5dbba2 ("bpf: Add a few optnames to bpf_setsockopt")
Signed-off-by: KaFai Wan <kafai.wan@linux.dev>
---
 net/core/filter.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/core/filter.c b/net/core/filter.c
index 5fa9189eb772..96849f4c1fbc 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5833,6 +5833,12 @@ BPF_CALL_5(bpf_sock_ops_setsockopt, struct bpf_sock_ops_kern *, bpf_sock,
 	if (!is_locked_tcp_sock_ops(bpf_sock))
 		return -EOPNOTSUPP;
 
+	/* TCP_NODELAY triggers tcp_push_pending_frames() and re-enters these callbacks. */
+	if ((bpf_sock->op == BPF_SOCK_OPS_HDR_OPT_LEN_CB ||
+	     bpf_sock->op == BPF_SOCK_OPS_WRITE_HDR_OPT_CB) &&
+	    level == SOL_TCP && optname == TCP_NODELAY)
+		return -EOPNOTSUPP;
+
 	return _bpf_setsockopt(bpf_sock->sk, level, optname, optval, optlen);
 }
 
-- 
2.43.0

[PATCH bpf v3 2/2] selftests/bpf: Test TCP_NODELAY in TCP hdr opt callbacks

[KaFai Wan]

Add a sockops selftest for the TCP_NODELAY restriction in
BPF_SOCK_OPS_HDR_OPT_LEN_CB and BPF_SOCK_OPS_WRITE_HDR_OPT_CB.

With BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG enabled,
bpf_setsockopt(TCP_NODELAY) returns -EOPNOTSUPP from
BPF_SOCK_OPS_HDR_OPT_LEN_CB and BPF_SOCK_OPS_WRITE_HDR_OPT_CB, avoiding
unbounded recursion and kernel stack overflow.

Other cases continue to work as before, including
BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB and user space
setsockopt(TCP_NODELAY).

Signed-off-by: KaFai Wan <kafai.wan@linux.dev>
---
 .../selftests/bpf/prog_tests/tcp_hdr_options.c    | 12 +++++++++++-
 .../bpf/progs/test_misc_tcp_hdr_options.c         | 15 ++++++++++++++-
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c b/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
index 56685fc03c7e..7b9dbbb84316 100644
--- a/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
+++ b/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
@@ -461,7 +461,7 @@ static void misc(void)
 	const unsigned int nr_data = 2;
 	struct bpf_link *link;
 	struct sk_fds sk_fds;
-	int i, ret;
+	int i, ret, true_val = 1;
 
 	lport_linum_map_fd = bpf_map__fd(misc_skel->maps.lport_linum_map);
 
@@ -477,6 +477,10 @@ static void misc(void)
 		return;
 	}
 
+	ret = setsockopt(sk_fds.active_fd, SOL_TCP, TCP_NODELAY, &true_val, sizeof(true_val));
+	if (!ASSERT_OK(ret, "setsockopt(TCP_NODELAY)"))
+		goto check_linum;
+
 	for (i = 0; i < nr_data; i++) {
 		/* MSG_EOR to ensure skb will not be combined */
 		ret = send(sk_fds.active_fd, send_msg, sizeof(send_msg),
@@ -507,6 +511,12 @@ static void misc(void)
 
 	ASSERT_EQ(misc_skel->bss->nr_hwtstamp, 0, "nr_hwtstamp");
 
+	ASSERT_TRUE(misc_skel->data->nodelay_est_ok, "unexpected nodelay_est_ok");
+
+	ASSERT_TRUE(misc_skel->data->nodelay_hdr_len_err, "unexpected nodelay_hdr_len_err");
+
+	ASSERT_TRUE(misc_skel->data->nodelay_write_hdr_err, "unexpected nodelay_write_hdr_err");
+
 check_linum:
 	ASSERT_FALSE(check_error_linum(&sk_fds), "check_error_linum");
 	sk_fds_close(&sk_fds);
diff --git a/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c b/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c
index d487153a839d..a02e28d9db2e 100644
--- a/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c
+++ b/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c
@@ -29,6 +29,10 @@ unsigned int nr_syn = 0;
 unsigned int nr_fin = 0;
 unsigned int nr_hwtstamp = 0;
 
+bool nodelay_est_ok = true;
+bool nodelay_hdr_len_err = true;
+bool nodelay_write_hdr_err = true;
+
 /* Check the header received from the active side */
 static int __check_active_hdr_in(struct bpf_sock_ops *skops, bool check_syn)
 {
@@ -300,7 +304,7 @@ static int handle_passive_estab(struct bpf_sock_ops *skops)
 SEC("sockops")
 int misc_estab(struct bpf_sock_ops *skops)
 {
-	int true_val = 1;
+	int true_val = 1, false_val = 0, ret;
 
 	switch (skops->op) {
 	case BPF_SOCK_OPS_TCP_LISTEN_CB:
@@ -316,10 +320,19 @@ int misc_estab(struct bpf_sock_ops *skops)
 	case BPF_SOCK_OPS_PARSE_HDR_OPT_CB:
 		return handle_parse_hdr(skops);
 	case BPF_SOCK_OPS_HDR_OPT_LEN_CB:
+		ret = bpf_setsockopt(skops, SOL_TCP, TCP_NODELAY, &true_val, sizeof(true_val));
+		nodelay_hdr_len_err &= ret == -EOPNOTSUPP;
+
 		return handle_hdr_opt_len(skops);
 	case BPF_SOCK_OPS_WRITE_HDR_OPT_CB:
+		ret = bpf_setsockopt(skops, SOL_TCP, TCP_NODELAY, &true_val, sizeof(true_val));
+		nodelay_write_hdr_err &= ret == -EOPNOTSUPP;
+
 		return handle_write_hdr_opt(skops);
 	case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
+		ret = bpf_setsockopt(skops, SOL_TCP, TCP_NODELAY, &false_val, sizeof(false_val));
+		nodelay_est_ok &= ret == 0;
+
 		return handle_passive_estab(skops);
 	}
 
-- 
2.43.0

Re: [PATCH bpf v3 1/2] bpf: Reject TCP_NODELAY in TCP header option callbacks

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 1997 bytes --]

> diff --git a/net/core/filter.c b/net/core/filter.c
> index 5fa9189eb772..96849f4c1fbc 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -5833,6 +5833,12 @@ BPF_CALL_5(bpf_sock_ops_setsockopt, struct bpf_sock_ops_kern *, bpf_sock,
>  	if (!is_locked_tcp_sock_ops(bpf_sock))
>  		return -EOPNOTSUPP;
>
> +	/* TCP_NODELAY triggers tcp_push_pending_frames() and re-enters these callbacks. */
> +	if ((bpf_sock->op == BPF_SOCK_OPS_HDR_OPT_LEN_CB ||
> +	     bpf_sock->op == BPF_SOCK_OPS_WRITE_HDR_OPT_CB) &&
> +	    level == SOL_TCP && optname == TCP_NODELAY)
> +		return -EOPNOTSUPP;
> +

Does this fix also need to block TCP_CORK? When bpf_setsockopt() is called
with SOL_TCP and TCP_CORK where the value is 0 (disabling cork), the call
path goes through:

bpf_sock_ops_setsockopt()
  -> _bpf_setsockopt()
    -> __bpf_setsockopt()
      -> sol_tcp_sockopt()
        -> do_tcp_setsockopt()
          -> __tcp_sock_set_cork(sk, false)

In __tcp_sock_set_cork() at net/ipv4/tcp.c, when cork is disabled, it
unconditionally calls tcp_push_pending_frames(sk):

net/ipv4/tcp.c:__tcp_sock_set_cork() {
    ...
    tcp->nonagle |= TCP_NAGLE_OFF|TCP_NAGLE_PUSH;

    tcp_push_pending_frames(sk);
}

This triggers the same recursion chain described in the commit message:

tcp_push_pending_frames()
  -> tcp_current_mss()
    -> tcp_established_options()
      -> bpf_skops_hdr_opt_len()
        -> BPF_CGROUP_RUN_PROG_SOCK_OPS_SK (re-enters with
           op=BPF_SOCK_OPS_HDR_OPT_LEN_CB)

causing unbounded recursion and kernel stack overflow. Note that enabling
TCP_CORK (val=1) is safe since it doesn't call tcp_push_pending_frames(),
only disabling it (val=0) does.


>  	return _bpf_setsockopt(bpf_sock->sk, level, optname, optval, optlen);
>  }


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/24558395229

Re: [PATCH bpf v3 1/2] bpf: Reject TCP_NODELAY in TCP header option callbacks

[Jiayuan Chen]

On 4/17/26 5:20 PM, KaFai Wan wrote:
> A BPF_SOCK_OPS program can enable
> BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG and then call
> bpf_setsockopt(TCP_NODELAY) from BPF_SOCK_OPS_HDR_OPT_LEN_CB or
> BPF_SOCK_OPS_WRITE_HDR_OPT_CB.
>
> In these callbacks, bpf_setsockopt(TCP_NODELAY) can reach
> __tcp_sock_set_nodelay(), which can call tcp_push_pending_frames().
>
>  From BPF_SOCK_OPS_HDR_OPT_LEN_CB, tcp_push_pending_frames() can call
> tcp_current_mss(), which calls tcp_established_options() and re-enters
> bpf_skops_hdr_opt_len().
>
> BPF_SOCK_OPS_HDR_OPT_LEN_CB
>    -> bpf_setsockopt(TCP_NODELAY)
>      -> tcp_push_pending_frames()
>        -> tcp_current_mss()
>          -> tcp_established_options()
>            -> bpf_skops_hdr_opt_len()
>              -> BPF_SOCK_OPS_HDR_OPT_LEN_CB
>
>  From BPF_SOCK_OPS_WRITE_HDR_OPT_CB, tcp_push_pending_frames() can call
> tcp_write_xmit(), which calls tcp_transmit_skb().  That path recomputes
> header option length through tcp_established_options() and
> bpf_skops_hdr_opt_len() before re-entering bpf_skops_write_hdr_opt().
>
> BPF_SOCK_OPS_WRITE_HDR_OPT_CB
>    -> bpf_setsockopt(TCP_NODELAY)
>      -> tcp_push_pending_frames()
>        -> tcp_write_xmit()
>          -> tcp_transmit_skb()
>            -> tcp_established_options()
>              -> bpf_skops_hdr_opt_len()
>            -> bpf_skops_write_hdr_opt()
>              -> BPF_SOCK_OPS_WRITE_HDR_OPT_CB
>
> This leads to unbounded recursion and can overflow the kernel stack.
>
> Reject TCP_NODELAY with -EOPNOTSUPP in bpf_sock_ops_setsockopt()
> when bpf_setsockopt() is called from
> BPF_SOCK_OPS_HDR_OPT_LEN_CB or BPF_SOCK_OPS_WRITE_HDR_OPT_CB.
>
> Reported-by: Quan Sun <2022090917019@std.uestc.edu.cn>
> Reported-by: Yinhao Hu <dddddd@hust.edu.cn>
> Reported-by: Kaiyan Mei <M202472210@hust.edu.cn>
> Closes: https://lore.kernel.org/bpf/d1d523c9-6901-4454-a183-94462b8f3e4e@std.uestc.edu.cn/
> Fixes: 7e41df5dbba2 ("bpf: Add a few optnames to bpf_setsockopt")
> Signed-off-by: KaFai Wan <kafai.wan@linux.dev>


Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>

I think the result of AI review is false-positve.

Re: [PATCH bpf v3 2/2] selftests/bpf: Test TCP_NODELAY in TCP hdr opt callbacks

[Jiayuan Chen]

On 4/17/26 5:20 PM, KaFai Wan wrote:
> Add a sockops selftest for the TCP_NODELAY restriction in
> BPF_SOCK_OPS_HDR_OPT_LEN_CB and BPF_SOCK_OPS_WRITE_HDR_OPT_CB.
>
> With BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG enabled,
> bpf_setsockopt(TCP_NODELAY) returns -EOPNOTSUPP from
> BPF_SOCK_OPS_HDR_OPT_LEN_CB and BPF_SOCK_OPS_WRITE_HDR_OPT_CB, avoiding
> unbounded recursion and kernel stack overflow.
>
> Other cases continue to work as before, including
> BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB and user space
> setsockopt(TCP_NODELAY).
>
> Signed-off-by: KaFai Wan <kafai.wan@linux.dev>


Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>


A little nit below, no need to resend.

> ---
>   .../selftests/bpf/prog_tests/tcp_hdr_options.c    | 12 +++++++++++-
>   .../bpf/progs/test_misc_tcp_hdr_options.c         | 15 ++++++++++++++-
>   2 files changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c b/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
> index 56685fc03c7e..7b9dbbb84316 100644
> --- a/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
> +++ b/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
> @@ -461,7 +461,7 @@ static void misc(void)
>   	const unsigned int nr_data = 2;
>   	struct bpf_link *link;
>   	struct sk_fds sk_fds;
> -	int i, ret;
> +	int i, ret, true_val = 1;
>   

NIT: please follow the reverse xmas tree variable ordering


>   	lport_linum_map_fd = bpf_map__fd(misc_skel->maps.lport_linum_map);
>   
> @@ -477,6 +477,10 @@ static void misc(void)
>   		return;
>   	}
>   
> +	ret = setsockopt(sk_fds.active_fd, SOL_TCP, TCP_NODELAY, &true_val, sizeof(true_val));
> +	if (!ASSERT_OK(ret, "setsockopt(TCP_NODELAY)"))
> +		goto check_linum;
> +
>   	for (i = 0; i < nr_data; i++) {
>   		/* MSG_EOR to ensure skb will not be combined */
>   		ret = send(sk_fds.active_fd, send_msg, sizeof(send_msg),
> @@ -507,6 +511,12 @@ static void misc(void)
>   
>   	ASSERT_EQ(misc_skel->bss->nr_hwtstamp, 0, "nr_hwtstamp");
>   
> +	ASSERT_TRUE(misc_skel->data->nodelay_est_ok, "unexpected nodelay_est_ok");
> +
> +	ASSERT_TRUE(misc_skel->data->nodelay_hdr_len_err, "unexpected nodelay_hdr_len_err");
> +
> +	ASSERT_TRUE(misc_skel->data->nodelay_write_hdr_err, "unexpected nodelay_write_hdr_err");
> +

NIT: It's would be misleading if you run ./test_progs with "-v"
misc:PASS:unexpected nodelay_est_ok 0 nsec

"PASS:unexpected" ?

>   check_linum:
>   	ASSERT_FALSE(check_error_linum(&sk_fds), "check_error_linum");
>   	sk_fds_close(&sk_fds);
> diff --git a/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c b/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c
> index d487153a839d..a02e28d9db2e 100644
> --- a/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c
> +++ b/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c
> @@ -29,6 +29,10 @@ unsigned int nr_syn = 0;
>   unsigned int nr_fin = 0;
>   unsigned int nr_hwtstamp = 0;
>   
> +bool nodelay_est_ok = true;
> +bool nodelay_hdr_len_err = true;
> +bool nodelay_write_hdr_err = true;

I prefer "nodelay_hdr_len_reject"

Re: [PATCH bpf v3 2/2] selftests/bpf: Test TCP_NODELAY in TCP hdr opt callbacks

[Martin KaFai Lau]

On Fri, Apr 17, 2026 at 05:20:35PM +0800, KaFai Wan wrote:
> diff --git a/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c b/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
> index 56685fc03c7e..7b9dbbb84316 100644
> --- a/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
> +++ b/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
> @@ -461,7 +461,7 @@ static void misc(void)
>  	const unsigned int nr_data = 2;
>  	struct bpf_link *link;
>  	struct sk_fds sk_fds;
> -	int i, ret;
> +	int i, ret, true_val = 1;
>  
>  	lport_linum_map_fd = bpf_map__fd(misc_skel->maps.lport_linum_map);
>  
> @@ -477,6 +477,10 @@ static void misc(void)
>  		return;
>  	}
>  
> +	ret = setsockopt(sk_fds.active_fd, SOL_TCP, TCP_NODELAY, &true_val, sizeof(true_val));

Same comment as in v2. Why this setsockopt is needed?
The setsockopt in userspace is unnecessary. In the future,
we may need to understand why it is needed here in the first place.