[PATCH] scsi: target: tcm_fc: use kref_get_unless_zero() in ft_sess_get()

ft_sess_get() walks the RCU-protected session hash under rcu_read_lock()
and takes a plain kref_get() on a matching session. Session teardown does
hlist_del_rcu() and then drops ft_lport_lock before the final
ft_sess_put() -> kfree_rcu(). A reader that is preempted between the
port_id comparison and the kref_get() can therefore revive a session whose
refcount has already dropped to zero and is pending free, leading to a
use-after-free and a double target_remove_session().

Use kref_get_unless_zero() and treat a zero refcount as "not found",
matching the standard pattern for RCU lookups that race with kref-based
teardown.

Fixes: 3699d92a4d7b ("[SCSI] tcm_fc: Adding FC_FC4 provider (tcm_fc) for FCoE target (TCM - target core) support")
Cc: [email protected]
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Yifei Gao <[email protected]>
---
 drivers/target/tcm_fc/tfc_sess.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/target/tcm_fc/tfc_sess.c b/drivers/target/tcm_fc/tfc_sess.c
index 797be06ab71b..1bc7d2dcbea3 100644
--- a/drivers/target/tcm_fc/tfc_sess.c
+++ b/drivers/target/tcm_fc/tfc_sess.c
@@ -172,7 +172,8 @@ static struct ft_sess *ft_sess_get(struct fc_lport *lport, u32 port_id)
 	head = &tport->hash[ft_sess_hash(port_id)];
 	hlist_for_each_entry_rcu(sess, head, hash) {
 		if (sess->port_id == port_id) {
-			kref_get(&sess->kref);
+			if (!kref_get_unless_zero(&sess->kref))
+				break;
 			rcu_read_unlock();
 			TFC_SESS_DBG(lport, "port_id %x found %p\n",
 				     port_id, sess);
-- 
2.43.0