[PATCH v9 4/9] gpio: cdev: Leverage revocable for accessing struct gpio_chip

Tzung-Bi Shih
2026-04-27T13:59:45Z

Struct gpio_device now provides a revocable provider to the underlying
struct gpio_chip. Leverage revocable for accessing the struct
gpio_chip.

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
v9:
- New to the series.
- Rename "chip_rp" -> "chip_rev".

v4 - v8:
- Doesn't exist.

v3: https://lore.kernel.org/all/20260213092958.864411-9-tzungbi@kernel.org
- Change revocable API usages accordingly.

v2: https://lore.kernel.org/all/20260203061059.975605-9-tzungbi@kernel.org
- Change usages accordingly after applying
https://lore.kernel.org/all/20260129143733.45618-4-tzungbi@kernel.org.
- Preserve a local storage for `struct revocable`.
- Combine multiple patches (see "v1:").
- Fix a race condition reported in
https://lore.kernel.org/all/CAMRc=McDaipt85OHm0MksLkuf6E79dY1uNSqqbcJnoQTUs81Pw@mail.gmail.com/
and analyzed in
https://lore.kernel.org/all/aXEEUWwkxHZzCnaI@tzungbi-laptop/.
In v1, the blocking_notifier_chain_unregister() will be skipped if the
chip has been removed, leading an UAF in gpiolib_cdev_unregister().
In v2, it won't skip blocking_notifier_chain_unregister().

v1:
- https://lore.kernel.org/all/20260116081036.352286-14-tzungbi@kernel.org
- https://lore.kernel.org/all/20260116081036.352286-15-tzungbi@kernel.org
- https://lore.kernel.org/all/20260116081036.352286-16-tzungbi@kernel.org
- https://lore.kernel.org/all/20260116081036.352286-17-tzungbi@kernel.org
- https://lore.kernel.org/all/20260116081036.352286-18-tzungbi@kernel.org

---
drivers/gpio/gpiolib-cdev.c | 68 ++++++++++++++-----------------------
1 file changed, 26 insertions(+), 42 deletions(-)

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index f36b7c06996d..d8a7ccb406a5 100644
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -22,6 +22,7 @@
#include <linux/overflow.h>
#include <linux/pinctrl/consumer.h>
#include <linux/poll.h>
+#include <linux/revocable.h>
#include <linux/seq_file.h>
#include <linux/spinlock.h>
#include <linux/string.h>
@@ -210,11 +211,9 @@ static long linehandle_ioctl(struct file *file, unsigned int cmd,
DECLARE_BITMAP(vals, GPIOHANDLES_MAX);
unsigned int i;
int ret;
+ struct gpio_chip *gc;

- guard(srcu)(&lh->gdev->srcu);
-
- if (!rcu_access_pointer(lh->gdev->chip))
- return -ENODEV;
+ revocable_try_access_or_return(&lh->gdev->chip_rev, gc);

switch (cmd) {
case GPIOHANDLE_GET_LINE_VALUES_IOCTL:
@@ -1432,11 +1431,9 @@ static long linereq_ioctl(struct file *file, unsigned int cmd,
{
struct linereq *lr = file->private_data;
void __user *ip = (void __user *)arg;
+ struct gpio_chip *gc;

- guard(srcu)(&lr->gdev->srcu);
-
- if (!rcu_access_pointer(lr->gdev->chip))
- return -ENODEV;
+ revocable_try_access_or_return(&lr->gdev->chip_rev, gc);

switch (cmd) {
case GPIO_V2_LINE_GET_VALUES_IOCTL:
@@ -1463,10 +1460,10 @@ static __poll_t linereq_poll(struct file *file,
{
struct linereq *lr = file->private_data;
__poll_t events = 0;
+ struct gpio_chip *gc;

- guard(srcu)(&lr->gdev->srcu);
-
- if (!rcu_access_pointer(lr->gdev->chip))
+ revocable_try_access_with(&lr->gdev->chip_rev, gc);
+ if (!gc)
return EPOLLHUP | EPOLLERR;

poll_wait(file, &lr->wait, wait);
@@ -1485,11 +1482,9 @@ static ssize_t linereq_read(struct file *file, char __user *buf,
struct gpio_v2_line_event le;
ssize_t bytes_read = 0;
int ret;
+ struct gpio_chip *gc;

- guard(srcu)(&lr->gdev->srcu);
-
- if (!rcu_access_pointer(lr->gdev->chip))
- return -ENODEV;
+ revocable_try_access_or_return(&lr->gdev->chip_rev, gc);

if (count < sizeof(le))
return -EINVAL;
@@ -1759,10 +1754,10 @@ static __poll_t lineevent_poll(struct file *file,
{
struct lineevent_state *le = file->private_data;
__poll_t events = 0;
+ struct gpio_chip *gc;

- guard(srcu)(&le->gdev->srcu);
-
- if (!rcu_access_pointer(le->gdev->chip))
+ revocable_try_access_with(&le->gdev->chip_rev, gc);
+ if (!gc)
return EPOLLHUP | EPOLLERR;

poll_wait(file, &le->wait, wait);
@@ -1797,11 +1792,9 @@ static ssize_t lineevent_read(struct file *file, char __user *buf,
ssize_t bytes_read = 0;
ssize_t ge_size;
int ret;
+ struct gpio_chip *gc;

- guard(srcu)(&le->gdev->srcu);
-
- if (!rcu_access_pointer(le->gdev->chip))
- return -ENODEV;
+ revocable_try_access_or_return(&le->gdev->chip_rev, gc);

/*
* When compatible system call is being used the struct gpioevent_data,
@@ -1879,11 +1872,9 @@ static long lineevent_ioctl(struct file *file, unsigned int cmd,
struct lineevent_state *le = file->private_data;
void __user *ip = (void __user *)arg;
struct gpiohandle_data ghd;
+ struct gpio_chip *gc;

- guard(srcu)(&le->gdev->srcu);
-
- if (!rcu_access_pointer(le->gdev->chip))
- return -ENODEV;
+ revocable_try_access_or_return(&le->gdev->chip_rev, gc);

/*
* We can get the value for an event line but not set it,
@@ -2385,12 +2376,10 @@ static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
struct gpio_chardev_data *cdev = file->private_data;
struct gpio_device *gdev = cdev->gdev;
void __user *ip = (void __user *)arg;
-
- guard(srcu)(&gdev->srcu);
+ struct gpio_chip *gc;

/* We fail any subsequent ioctl():s when the chip is gone */
- if (!rcu_access_pointer(gdev->chip))
- return -ENODEV;
+ revocable_try_access_or_return(&gdev->chip_rev, gc);

/* Fill in the struct and pass to userspace */
switch (cmd) {
@@ -2448,12 +2437,9 @@ static void lineinfo_changed_func(struct work_struct *work)
* Pin functions are in general much more static and while it's
* not 100% bullet-proof, it's good enough for most cases.
*/
- scoped_guard(srcu, &ctx->gdev->srcu) {
- gc = srcu_dereference(ctx->gdev->chip, &ctx->gdev->srcu);
- if (gc &&
- !pinctrl_gpio_can_use_line(gc, ctx->chg.info.offset))
+ revocable_try_access_or_skip_scoped(&ctx->gdev->chip_rev, gc)
+ if (!pinctrl_gpio_can_use_line(gc, ctx->chg.info.offset))
ctx->chg.info.flags |= GPIO_V2_LINE_FLAG_USED;
- }
}

ret = kfifo_in_spinlocked(&ctx->cdev->events, &ctx->chg, 1,
@@ -2534,10 +2520,10 @@ static __poll_t lineinfo_watch_poll(struct file *file,
{
struct gpio_chardev_data *cdev = file->private_data;
__poll_t events = 0;
+ struct gpio_chip *gc;

- guard(srcu)(&cdev->gdev->srcu);
-
- if (!rcu_access_pointer(cdev->gdev->chip))
+ revocable_try_access_with(&cdev->gdev->chip_rev, gc);
+ if (!gc)
return EPOLLHUP | EPOLLERR;

poll_wait(file, &cdev->wait, pollt);
@@ -2557,11 +2543,9 @@ static ssize_t lineinfo_watch_read(struct file *file, char __user *buf,
ssize_t bytes_read = 0;
int ret;
size_t event_size;
+ struct gpio_chip *gc;

- guard(srcu)(&cdev->gdev->srcu);
-
- if (!rcu_access_pointer(cdev->gdev->chip))
- return -ENODEV;
+ revocable_try_access_or_return(&cdev->gdev->chip_rev, gc);

#ifndef CONFIG_GPIO_CDEV_V1
event_size = sizeof(struct gpio_v2_line_info_changed);
--
2.51.0