Add a check to ensure that `x25_sock.fraglen` does not overflow.

The `fraglen` also needs to be resetted when purging `fragment_queue` in
`x25_clear_queues()`.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Suggested-by: Yiming Qian <yimingqian591@gmail.com>
Signed-off-by: Martin Schiller <ms@dev.tdt.de>
---
Changes in v3:
- Added missing Cc: Simon Horman <horms@kernel.org>  
- Added missing Fixes tag
- Replaced `Reported-by:` by `Suggested-by:`, because I cannot give an
  URL to the required `Closes:` tag
- Link to v2: https://lore.kernel.org/r/20260327-x25_fraglen-v2-1-143911c3f62a@dev.tdt.de

Changes in v2:
- Use USHRT_MAX instead of sizeof(fraglen) nonsense
- Link to v1: https://lore.kernel.org/r/20260327-x25_fraglen-v1-1-9fc751d4f754@dev.tdt.de
---
 net/x25/x25_in.c   | 6 ++++++
 net/x25/x25_subr.c | 1 +
 2 files changed, 7 insertions(+)

diff --git a/net/x25/x25_in.c b/net/x25/x25_in.c
index b981a4828d08c2e6676749a06035910eab01e6cd..cb84c683d249d6078f3673835bb2f80eb487f253 100644
--- a/net/x25/x25_in.c
+++ b/net/x25/x25_in.c
@@ -34,6 +34,12 @@ static int x25_queue_rx_frame(struct sock *sk, struct sk_buff *skb, int more)
 	struct sk_buff *skbo, *skbn = skb;
 	struct x25_sock *x25 = x25_sk(sk);
 
+	/* make sure we don't overflow */
+	if (x25->fraglen + skb->len > USHRT_MAX) {
+		kfree_skb(skb);
+		return 1;
+	}
+
 	if (more) {
 		x25->fraglen += skb->len;
 		skb_queue_tail(&x25->fragment_queue, skb);
diff --git a/net/x25/x25_subr.c b/net/x25/x25_subr.c
index 0285aaa1e93c17233748d38eef6d8b5c6059b67a..159708d9ad20cb2e6db24ead67daf1e9d6258f64 100644
--- a/net/x25/x25_subr.c
+++ b/net/x25/x25_subr.c
@@ -40,6 +40,7 @@ void x25_clear_queues(struct sock *sk)
 	skb_queue_purge(&x25->interrupt_in_queue);
 	skb_queue_purge(&x25->interrupt_out_queue);
 	skb_queue_purge(&x25->fragment_queue);
+	x25->fraglen = 0;
 }
 
 

---
base-commit: dc9e9d61e301c087bcd990dbf2fa18ad3e2e1429
change-id: 20260325-x25_fraglen-8fc240d1edd3

Best regards,
-- 
Martin Schiller <ms@dev.tdt.de>