[PATCH v1 net 1/2] tcp: Clear tcp_sk(sk)->fastopen_rsk in tcp_disconnect().

[Kuniyuki Iwashima]

syzbot reported the splat below where a socket had tcp_sk(sk)->fastopen_rsk
in the TCP_ESTABLISHED state. [0]

syzbot reused the server-side TCP Fast Open socket as a new client before
the TFO socket completes 3WHS:

1. accept()
2. connect(AF_UNSPEC)
3. connect() to another destination

As of accept(), sk->sk_state is TCP_SYN_RECV, and tcp_disconnect() changes
it to TCP_CLOSE and makes connect() possible, which restarts timers.

Since tcp_disconnect() forgot to clear tcp_sk(sk)->fastopen_rsk, the
retransmit timer triggered the warning and the intended packet was not
retransmitted.

Let's call reqsk_fastopen_remove() in tcp_disconnect().

[0]:
WARNING: CPU: 2 PID: 0 at net/ipv4/tcp_timer.c:542 tcp_retransmit_timer (net/ipv4/tcp_timer.c:542 (discriminator 7))
Modules linked in:
CPU: 2 UID: 0 PID: 0 Comm: swapper/2 Not tainted 6.17.0-rc5-g201825fb4278 #62 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:tcp_retransmit_timer (net/ipv4/tcp_timer.c:542 (discriminator 7))
Code: 41 55 41 54 55 53 48 8b af b8 08 00 00 48 89 fb 48 85 ed 0f 84 55 01 00 00 0f b6 47 12 3c 03 74 0c 0f b6 47 12 3c 04 74 04 90 <0f> 0b 90 48 8b 85 c0 00 00 00 48 89 ef 48 8b 40 30 e8 6a 4f 06 3e
RSP: 0018:ffffc900002f8d40 EFLAGS: 00010293
RAX: 0000000000000002 RBX: ffff888106911400 RCX: 0000000000000017
RDX: 0000000002517619 RSI: ffffffff83764080 RDI: ffff888106911400
RBP: ffff888106d5c000 R08: 0000000000000001 R09: ffffc900002f8de8
R10: 00000000000000c2 R11: ffffc900002f8ff8 R12: ffff888106911540
R13: ffff888106911480 R14: ffff888106911840 R15: ffffc900002f8de0
FS: 0000000000000000(0000) GS:ffff88907b768000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8044d69d90 CR3: 0000000002c30003 CR4: 0000000000370ef0
Call Trace:
<IRQ>
tcp_write_timer (net/ipv4/tcp_timer.c:738)
call_timer_fn (kernel/time/timer.c:1747)
__run_timers (kernel/time/timer.c:1799 kernel/time/timer.c:2372)
timer_expire_remote (kernel/time/timer.c:2385 kernel/time/timer.c:2376 kernel/time/timer.c:2135)
tmigr_handle_remote_up (kernel/time/timer_migration.c:944 kernel/time/timer_migration.c:1035)
__walk_groups.isra.0 (kernel/time/timer_migration.c:533 (discriminator 1))
tmigr_handle_remote (kernel/time/timer_migration.c:1096)
handle_softirqs (./arch/x86/include/asm/jump_label.h:36 ./include/trace/events/irq.h:142 kernel/softirq.c:580)
irq_exit_rcu (kernel/softirq.c:614 kernel/softirq.c:453 kernel/softirq.c:680 kernel/softirq.c:696)
sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1050 (discriminator 35) arch/x86/kernel/apic/apic.c:1050 (discriminator 35))
</IRQ>

Fixes: 8336886f786f ("tcp: TCP Fast Open Server - support TFO listeners")
Reported-by: syzkaller <syzk...@googlegroups.com>
Signed-off-by: Kuniyuki Iwashima <kun...@google.com>
---
net/ipv4/tcp.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 71a956fbfc55..ad76556800f2 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3327,6 +3327,7 @@ int tcp_disconnect(struct sock *sk, int flags)
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int old_state = sk->sk_state;
+ struct request_sock *req;
u32 seq;

if (old_state != TCP_CLOSE)
@@ -3442,6 +3443,10 @@ int tcp_disconnect(struct sock *sk, int flags)


/* Clean up fastopen related fields */
+ req = rcu_dereference_protected(tp->fastopen_rsk,
+ lockdep_sock_is_held(sk));
+ if (req)
+ reqsk_fastopen_remove(sk, req, false);
tcp_free_fastopen_req(tp);
inet_clear_bit(DEFER_CONNECT, sk);
tp->fastopen_client_fail = 0;
--
2.51.0.384.g4c02a37b29-goog

[Greg Kroah-Hartman]

6.1-stable review patch. If anyone has any objections, please let me know.

------------------

From: Kuniyuki Iwashima <kun...@google.com>

[ Upstream commit 45c8a6cc2bcd780e634a6ba8e46bffbdf1fc5c01 ]

Link: https://patch.msgid.link/20250915175800....@google.com
Signed-off-by: Jakub Kicinski <ku...@kernel.org>
Signed-off-by: Sasha Levin <sas...@kernel.org>

---
net/ipv4/tcp.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c

index b64d53590f25c..d94daa296d59d 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3130,6 +3130,7 @@ int tcp_disconnect(struct sock *sk, int flags)

struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int old_state = sk->sk_state;
+ struct request_sock *req;
u32 seq;

if (old_state != TCP_CLOSE)

@@ -3239,6 +3240,10 @@ int tcp_disconnect(struct sock *sk, int flags)

/* Clean up fastopen related fields */
+ req = rcu_dereference_protected(tp->fastopen_rsk,
+ lockdep_sock_is_held(sk));
+ if (req)
+ reqsk_fastopen_remove(sk, req, false);
tcp_free_fastopen_req(tp);

inet->defer_connect = 0;

[Greg Kroah-Hartman]

6.6-stable review patch. If anyone has any objections, please let me know.

index a4bbe959d1e25..40a2f172be2cb 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3011,6 +3011,7 @@ int tcp_disconnect(struct sock *sk, int flags)

struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int old_state = sk->sk_state;
+ struct request_sock *req;
u32 seq;

if (old_state != TCP_CLOSE)

@@ -3121,6 +3122,10 @@ int tcp_disconnect(struct sock *sk, int flags)

/* Clean up fastopen related fields */
+ req = rcu_dereference_protected(tp->fastopen_rsk,
+ lockdep_sock_is_held(sk));
+ if (req)
+ reqsk_fastopen_remove(sk, req, false);
tcp_free_fastopen_req(tp);

inet_clear_bit(DEFER_CONNECT, sk);

[Greg Kroah-Hartman]

6.12-stable review patch. If anyone has any objections, please let me know.

index 156da81bce068..988992ff898b3 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3286,6 +3286,7 @@ int tcp_disconnect(struct sock *sk, int flags)

struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int old_state = sk->sk_state;
+ struct request_sock *req;
u32 seq;

if (old_state != TCP_CLOSE)

@@ -3400,6 +3401,10 @@ int tcp_disconnect(struct sock *sk, int flags)

[Greg Kroah-Hartman]

6.16-stable review patch. If anyone has any objections, please let me know.

index 461a9ab540af0..98da33e0c308b 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3330,6 +3330,7 @@ int tcp_disconnect(struct sock *sk, int flags)

struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int old_state = sk->sk_state;
+ struct request_sock *req;
u32 seq;

if (old_state != TCP_CLOSE)

@@ -3445,6 +3446,10 @@ int tcp_disconnect(struct sock *sk, int flags)