[PATCH net 1/1] sctp: diag: reject stale associations in dump_one path

From: Zhao Zhang <[email protected]>

The SCTP exact sock_diag lookup can hold a transport reference, block on
lock_sock(sk), and then resume after sctp_association_free() has marked
the association dead and freed its bind address list.

When that happens, inet_assoc_attr_size() and
inet_diag_msg_sctpasoc_fill() can still dereference association state
that is no longer valid for reporting. In particular,
inet_diag_msg_sctpasoc_fill() may read an empty bind-address list as a
real sctp_sockaddr_entry and trigger an out-of-bounds read from
unrelated association memory.

Reject the association after taking the socket lock if it has been
reaped or detached from the endpoint, and report the lookup as stale.
This keeps the exact dump-one path from formatting torn association
state.

Fixes: 8f840e47f190 ("sctp: add the sctp_diag.c file")
Cc: [email protected]
Reported-by: Yuan Tan <[email protected]>
Reported-by: Yifan Wu <[email protected]>
Reported-by: Juefei Pu <[email protected]>
Reported-by: Zhengchuan Liang <[email protected]>
Reported-by: Xin Liu <[email protected]>
Assisted-by: Codex:GPT-5.4
Signed-off-by: Zhao Zhang <[email protected]>
Signed-off-by: Ren Wei <[email protected]>
---
 net/sctp/diag.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/net/sctp/diag.c b/net/sctp/diag.c
index 2afb376299fe..d758f5c3e06e 100644
--- a/net/sctp/diag.c
+++ b/net/sctp/diag.c
@@ -266,15 +266,15 @@ static int sctp_sock_dump_one(struct sctp_endpoint *ep, struct sctp_transport *t
 
 	lock_sock(sk);
 
-	rep = nlmsg_new(inet_assoc_attr_size(sk, assoc), GFP_KERNEL);
-	if (!rep) {
-		release_sock(sk);
-		return -ENOMEM;
+	if (ep != assoc->ep || assoc->base.dead) {
+		err = -ESTALE;
+		goto out_unlock;
 	}
 
-	if (ep != assoc->ep) {
-		err = -EAGAIN;
-		goto out;
+	rep = nlmsg_new(inet_assoc_attr_size(sk, assoc), GFP_KERNEL);
+	if (!rep) {
+		err = -ENOMEM;
+		goto out_unlock;
 	}
 
 	err = inet_sctp_diag_fill(sk, assoc, rep, req, sk_user_ns(NETLINK_CB(skb).sk),
@@ -289,8 +289,9 @@ static int sctp_sock_dump_one(struct sctp_endpoint *ep, struct sctp_transport *t
 	return nlmsg_unicast(sock_net(skb->sk)->diag_nlsk, rep, NETLINK_CB(skb).portid);
 
 out:
-	release_sock(sk);
 	kfree_skb(rep);
+out_unlock:
+	release_sock(sk);
 	return err;
 }
 
-- 
2.47.3