gpiolib: fix race condition for gdev->srcu

If two drivers were calling gpiochip_add_data_with_key(), one may be
traversing the srcu-protected list in gpio_name_to_desc(), meanwhile
other has just added its gdev in gpiodev_add_to_list_unlocked().
This creates a non-mutexed and non-protected timeframe, when one
instance is dereferencing and using &gdev->srcu, before the other
has initialized it, resulting in crash:

[    4.935481] Unable to handle kernel paging request at virtual address ffff800272bcc000
[    4.943396] Mem abort info:
[    4.943400]   ESR = 0x0000000096000005
[    4.943403]   EC = 0x25: DABT (current EL), IL = 32 bits
[    4.943407]   SET = 0, FnV = 0
[    4.943410]   EA = 0, S1PTW = 0
[    4.943413]   FSC = 0x05: level 1 translation fault
[    4.943416] Data abort info:
[    4.943418]   ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
[    4.946220]   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[    4.955261]   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[    4.955268] swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000000038e6c000
[    4.961449] [ffff800272bcc000] pgd=0000000000000000
[    4.969203] , p4d=1000000039739003
[    4.979730] , pud=0000000000000000
[    4.980210] phandle (CPU): 0x0000005e, phandle (BE): 0x5e000000 for node "reset"
[    4.991736] Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
...
[    5.121359] pc : __srcu_read_lock+0x44/0x98
[    5.131091] lr : gpio_name_to_desc+0x60/0x1a0
[    5.153671] sp : ffff8000833bb430
[    5.298440]
[    5.298443] Call trace:
[    5.298445]  __srcu_read_lock+0x44/0x98
[    5.309484]  gpio_name_to_desc+0x60/0x1a0
[    5.320692]  gpiochip_add_data_with_key+0x488/0xf00
    5.946419] ---[ end trace 0000000000000000 ]---

Move initialization code for gdev fields before it is added to
gpio_devices, with adjacent initialization code.
Adjust goto statements  to reflect modified order of operations

Fixes: 47d8b4c1d868 ("gpio: add SRCU infrastructure to struct gpio_device")
Reviewed-by: Jakub Lewalski <jakub.lewalski@nokia.com>
Signed-off-by: Paweł Narewski <pawel.narewski@nokia.com>
[Bartosz: fixed a build issue, removed stray newline]
Link: https://lore.kernel.org/r/20251224082641.10769-1-bartosz.golaszewski@oss.qualcomm.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 9ccfb7af67cca61207e8479842b78942a22cb919..c06152b16dbc77b827ebad49a9df52fcce527592 100644 (file)
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1105,6 +1105,18 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
        gdev->ngpio = gc->ngpio;
        gdev->can_sleep = gc->can_sleep;
 
+       rwlock_init(&gdev->line_state_lock);
+       RAW_INIT_NOTIFIER_HEAD(&gdev->line_state_notifier);
+       BLOCKING_INIT_NOTIFIER_HEAD(&gdev->device_notifier);
+
+       ret = init_srcu_struct(&gdev->srcu);
+       if (ret)
+               goto err_free_label;
+
+       ret = init_srcu_struct(&gdev->desc_srcu);
+       if (ret)
+               goto err_cleanup_gdev_srcu;
+
        scoped_guard(mutex, &gpio_devices_lock) {
                /*
                 * TODO: this allocates a Linux GPIO number base in the global
@@ -1119,7 +1131,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
                        if (base < 0) {
                                ret = base;
                                base = 0;
-                               goto err_free_label;
+                               goto err_cleanup_desc_srcu;
                        }
 
                        /*
@@ -1139,22 +1151,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
                ret = gpiodev_add_to_list_unlocked(gdev);
                if (ret) {
                        gpiochip_err(gc, "GPIO integer space overlap, cannot add chip\n");
-                       goto err_free_label;
+                       goto err_cleanup_desc_srcu;
                }
        }
 
-       rwlock_init(&gdev->line_state_lock);
-       RAW_INIT_NOTIFIER_HEAD(&gdev->line_state_notifier);
-       BLOCKING_INIT_NOTIFIER_HEAD(&gdev->device_notifier);
-
-       ret = init_srcu_struct(&gdev->srcu);
-       if (ret)
-               goto err_remove_from_list;
-
-       ret = init_srcu_struct(&gdev->desc_srcu);
-       if (ret)
-               goto err_cleanup_gdev_srcu;
-
 #ifdef CONFIG_PINCTRL
        INIT_LIST_HEAD(&gdev->pin_ranges);
 #endif
@@ -1164,11 +1164,11 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 
        ret = gpiochip_set_names(gc);
        if (ret)
-               goto err_cleanup_desc_srcu;
+               goto err_remove_from_list;
 
        ret = gpiochip_init_valid_mask(gc);
        if (ret)
-               goto err_cleanup_desc_srcu;
+               goto err_remove_from_list;
 
        for (desc_index = 0; desc_index < gc->ngpio; desc_index++) {
                struct gpio_desc *desc = &gdev->descs[desc_index];
@@ -1248,10 +1248,6 @@ err_remove_of_chip:
        of_gpiochip_remove(gc);
 err_free_valid_mask:
        gpiochip_free_valid_mask(gc);
-err_cleanup_desc_srcu:
-       cleanup_srcu_struct(&gdev->desc_srcu);
-err_cleanup_gdev_srcu:
-       cleanup_srcu_struct(&gdev->srcu);
 err_remove_from_list:
        scoped_guard(mutex, &gpio_devices_lock)
                list_del_rcu(&gdev->list);
@@ -1261,6 +1257,10 @@ err_remove_from_list:
                gpio_device_put(gdev);
                goto err_print_message;
        }
+err_cleanup_desc_srcu:
+       cleanup_srcu_struct(&gdev->desc_srcu);
+err_cleanup_gdev_srcu:
+       cleanup_srcu_struct(&gdev->srcu);
 err_free_label:
        kfree_const(gdev->label);
 err_free_descs: