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gpiolib: Fix possible use after free on label

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gpiod_request_commit() copies the pointer to the label passed as
an argument only to be used later. But there's a chance the caller
could immediately free the passed string(e.g., local variable).
This could trigger a use after free when we use gpio label(e.g.,
gpiochip_unlock_as_irq(), gpiochip_is_requested()).

To be on the safe side: duplicate the string with kstrdup_const()
so that if an unaware user passes an address to a stack-allocated
buffer, we won't get the arbitrary label.

Also fix gpiod_set_consumer_name().

Signed-off-by: Muchun Song <smuchun@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
This commit is contained in:
Muchun Song 2018-11-01 21:12:50 +08:00 committed by Linus Walleij
parent 02cb87f79b
commit 18534df419
2 changed files with 25 additions and 6 deletions
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25
drivers/gpio/gpiolib.c
View File

@ -2282,6 +2282,12 @@ static int gpiod_request_commit(struct gpio_desc *desc, const char *label)
unsigned long flags;
unsigned offset;
if (label) {
label = kstrdup_const(label, GFP_KERNEL);
if (!label)
return -ENOMEM;
}
spin_lock_irqsave(&gpio_lock, flags);
/* NOTE: gpio_request() can be called in early boot,
@ -2292,6 +2298,7 @@ static int gpiod_request_commit(struct gpio_desc *desc, const char *label)
desc_set_label(desc, label ? : "?");
status = 0;
} else {
kfree_const(label);
status = -EBUSY;
goto done;
}
@ -2308,6 +2315,7 @@ static int gpiod_request_commit(struct gpio_desc *desc, const char *label)
if (status < 0) {
desc_set_label(desc, NULL);
kfree_const(label);
clear_bit(FLAG_REQUESTED, &desc->flags);
goto done;
}
@ -2403,6 +2411,7 @@ static bool gpiod_free_commit(struct gpio_desc *desc)
chip->free(chip, gpio_chip_hwgpio(desc));
spin_lock_irqsave(&gpio_lock, flags);
}
kfree_const(desc->label);
desc_set_label(desc, NULL);
clear_bit(FLAG_ACTIVE_LOW, &desc->flags);
clear_bit(FLAG_REQUESTED, &desc->flags);
@ -3358,11 +3367,19 @@ EXPORT_SYMBOL_GPL(gpiod_cansleep);
* @desc: gpio to set the consumer name on
* @name: the new consumer name
*/
void gpiod_set_consumer_name(struct gpio_desc *desc, const char *name)
int gpiod_set_consumer_name(struct gpio_desc *desc, const char *name)
{
VALIDATE_DESC_VOID(desc);
/* Just overwrite whatever the previous name was */
desc->label = name;
VALIDATE_DESC(desc);
if (name) {
name = kstrdup_const(name, GFP_KERNEL);
if (!name)
return -ENOMEM;
}
kfree_const(desc->label);
desc_set_label(desc, name);
return 0;
}
EXPORT_SYMBOL_GPL(gpiod_set_consumer_name);

6
include/linux/gpio/consumer.h
View File

@ -162,7 +162,7 @@ int gpiod_is_active_low(const struct gpio_desc *desc);
int gpiod_cansleep(const struct gpio_desc *desc);
int gpiod_to_irq(const struct gpio_desc *desc);
void gpiod_set_consumer_name(struct gpio_desc *desc, const char *name);
int gpiod_set_consumer_name(struct gpio_desc *desc, const char *name);
/* Convert between the old gpio_ and new gpiod_ interfaces */
struct gpio_desc *gpio_to_desc(unsigned gpio);
@ -495,10 +495,12 @@ static inline int gpiod_to_irq(const struct gpio_desc *desc)
return -EINVAL;
}
static inline void gpiod_set_consumer_name(struct gpio_desc *desc, const char *name)
static inline int gpiod_set_consumer_name(struct gpio_desc *desc,
const char *name)
{
/* GPIO can never have been requested */
WARN_ON(1);
return -EINVAL;
}
static inline struct gpio_desc *gpio_to_desc(unsigned gpio)