[PATCH] drivers: block: rnbd: Handle generic ERR_PTR returns safely in find_and_get_or_create_sess()

[Ranganath V N <vnranganath.20@gmail.com>]

Fix the issue detected by the smatch tool.
drivers/block/rnbd/rnbd-clt.c:1241 find_and_get_or_create_sess()
error: 'sess' dereferencing possible ERR_PTR()

find_and_get_or_create_sess() only checks for ERR_PTR(-ENOMEM) after
calling find_or_create_sess(). In other encoded failures, the code
may dereference the error pointer when accessing sess->nr_poll_queues,
resulting ina kernel oops.

By preserving the existing -ENOMEM behaviour and log unexpected
errors to assist in debugging. This change eliminates a potential
invalid pointer dereference without altering the function's logic
or intenet.

Tested by compiling using smatch tool.

Signed-off-by: Ranganath V N <vnranganath.20@gmail.com>
---
 drivers/block/rnbd/rnbd-clt.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c
index f1409e54010a..57ca694210b9 100644
--- a/drivers/block/rnbd/rnbd-clt.c
+++ b/drivers/block/rnbd/rnbd-clt.c
@@ -1236,9 +1236,14 @@ find_and_get_or_create_sess(const char *sessname,
 	struct rtrs_clt_ops rtrs_ops;
 
 	sess = find_or_create_sess(sessname, &first);
-	if (sess == ERR_PTR(-ENOMEM)) {
-		return ERR_PTR(-ENOMEM);
-	} else if ((nr_poll_queues && !first) ||  (!nr_poll_queues && sess->nr_poll_queues)) {
+	if (IS_ERR(sess)) {
+		err = PTR_ERR(sess);
+		if (err != -ENOMEM)
+			pr_warn("rndb: find_or_create_sess(%s) failed with %d\n",
+				sessname, err);
+		return ERR_PTR(err);
+	}
+	if ((nr_poll_queues && !first) ||  (!nr_poll_queues && sess->nr_poll_queues)) {
 		/*
 		 * A device MUST have its own session to use the polling-mode.
 		 * It must fail to map new device with the same session.

---
base-commit: 211ddde0823f1442e4ad052a2f30f050145ccada
change-id: 20251021-rnbd_fix-9b478fb52403

Best regards,
-- 
Ranganath V N <vnranganath.20@gmail.com>