[PATCH] gpiolib: don't report -ENOMEM for a requested line without a label

[Adrian Ambrozewicz <aambrozewicz@nvidia.com>]

gpiod_request_commit() sets GPIOD_FLAG_REQUESTED, calls ->request() and
only then sets the label. A line in between has no label, so
gpiochip_dup_line_label() passes NULL to kstrdup() and returns
ERR_PTR(-ENOMEM), which for_each_hwgpio() then passes to kfree():

  BUG: unable to handle page fault for address: ffcc73074355ffc8
  Call Trace:
   gpio_sim_dbg_show
   gpiolib_seq_show
   seq_read_iter

Return NULL for such a line, as for an unrequested one.

Reproduced with gpio-sim: reading /sys/kernel/debug/gpio in a loop while
lines are requested and released oopses within seconds; with this
change, 100000 cycles pass.

Fixes: 35b545332b80 ("gpio: remove gpio_lock")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20261020-gpiolib-chip-removal-v3-0-aambrozewicz@nvidia.com?part=2
Assisted-by: LLM
Signed-off-by: Adrian Ambrozewicz <aambrozewicz@nvidia.com>
---
 drivers/gpio/gpiolib.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 1438f97d0634..9c05d36ccd74 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2721,6 +2721,7 @@ void gpiod_free(struct gpio_desc *desc)
 char *gpiochip_dup_line_label(struct gpio_chip *gc, unsigned int offset)
 {
 	struct gpio_desc *desc;
+	const char *name;
 	char *label;
 
 	desc = gpiochip_get_desc(gc, offset);
@@ -2732,7 +2733,11 @@ char *gpiochip_dup_line_label(struct gpio_chip *gc, unsigned int offset)
 
 	guard(srcu)(&desc->gdev->desc_srcu);
 
-	label = kstrdup(gpiod_get_label(desc), GFP_KERNEL);
+	name = gpiod_get_label(desc);
+	if (!name)
+		return NULL;
+
+	label = kstrdup(name, GFP_KERNEL);
 	if (!label)
 		return ERR_PTR(-ENOMEM);
 

base-commit: a0fe269293509acdd93b9cfb3f46636f7b91b33a
-- 
2.43.0