[PATCH net v3] tipc: fix divide-by-zero in tipc_sk_filter_connect()

[Mehul Rao <mehulrao@gmail.com>]

A user can set conn_timeout to any value via
setsockopt(TIPC_CONN_TIMEOUT), including values less than 4.  When a
SYN is rejected with TIPC_ERR_OVERLOAD and the retry path in
tipc_sk_filter_connect() executes:

    delay %= (tsk->conn_timeout / 4);

If conn_timeout is in the range [0, 3], the integer division yields 0,
and the modulo operation triggers a divide-by-zero exception, causing a
kernel oops/panic.

Fix this by clamping conn_timeout to a minimum of 4 at the point of use
in tipc_sk_filter_connect().

Oops: divide error: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 119 Comm: poc-F144 Not tainted 7.0.0-rc2+
RIP: 0010:tipc_sk_filter_rcv (net/tipc/socket.c:2236 net/tipc/socket.c:2362)
Call Trace:
 tipc_sk_backlog_rcv (include/linux/instrumented.h:82 include/linux/atomic/atomic-instrumented.h:32 include/net/sock.h:2357 net/tipc/socket.c:2406)
 __release_sock (include/net/sock.h:1185 net/core/sock.c:3213)
 release_sock (net/core/sock.c:3797)
 tipc_connect (net/tipc/socket.c:2570)
 __sys_connect (include/linux/file.h:62 include/linux/file.h:83 net/socket.c:2098)

Fixes: 6787927475e5 ("tipc: buffer overflow handling in listener socket")
Cc: stable@vger.kernel.org
Signed-off-by: Mehul Rao <mehulrao@gmail.com>
---
Changes in v3:
- Decode stack trace symbols (Eric Dumazet)
- Link to v2: https://lore.kernel.org/netdev/20260306185005.22120-1-mehulrao@gmail.com/

Changes in v2:
- Clamp conn_timeout at the point of use in tipc_sk_filter_connect()
  instead of rejecting small values in tipc_setsockopt()
- Link to v1: https://lore.kernel.org/netdev/20260305215336.645186-1-mehulrao@gmail.com/
---
 net/tipc/socket.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index 4c618c2b871d..9329919fb07f 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -2233,6 +2233,8 @@ static bool tipc_sk_filter_connect(struct tipc_sock *tsk, struct sk_buff *skb,
 		if (skb_queue_empty(&sk->sk_write_queue))
 			break;
 		get_random_bytes(&delay, 2);
+		if (tsk->conn_timeout < 4)
+			tsk->conn_timeout = 4;
 		delay %= (tsk->conn_timeout / 4);
 		delay = msecs_to_jiffies(delay + 100);
 		sk_reset_timer(sk, &sk->sk_timer, jiffies + delay);
-- 
2.53.0