'struct hidraw_list' is a circular queue whose head can be smaller than
tail. Using 'list->tail != list->head' to release all memory that should
be released.

Fixes: a5623a203cff ("HID: hidraw: fix memory leak in hidraw_release()")
Signed-off-by: Su Hui <suhui@nfschina.com>
---
 drivers/hid/hidraw.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/hidraw.c b/drivers/hid/hidraw.c
index 13c8dd8cd350..2bc762d31ac7 100644
--- a/drivers/hid/hidraw.c
+++ b/drivers/hid/hidraw.c
@@ -357,8 +357,11 @@ static int hidraw_release(struct inode * inode, struct file * file)
 	down_write(&minors_rwsem);
 
 	spin_lock_irqsave(&hidraw_table[minor]->list_lock, flags);
-	for (int i = list->tail; i < list->head; i++)
-		kfree(list->buffer[i].value);
+	while (list->tail != list->head) {
+		kfree(list->buffer[list->tail].value);
+		list->buffer[list->tail].value = NULL;
+		list->tail = (list->tail + 1) & (HIDRAW_BUFFER_SIZE - 1);
+	}
 	list_del(&list->node);
 	spin_unlock_irqrestore(&hidraw_table[minor]->list_lock, flags);
 	kfree(list);
-- 
2.30.2

On Thu, 25 Jan 2024, Su Hui wrote:

> 'struct hidraw_list' is a circular queue whose head can be smaller than
> tail. Using 'list->tail != list->head' to release all memory that should
> be released.
> 
> Fixes: a5623a203cff ("HID: hidraw: fix memory leak in hidraw_release()")
> Signed-off-by: Su Hui <suhui@nfschina.com>

Good catch, thanks. Applied.

-- 
Jiri Kosina
SUSE Labs

On Thu, Jan 25, 2024 at 02:32:26PM +0800, Su Hui wrote:
> 'struct hidraw_list' is a circular queue whose head can be smaller than
> tail. Using 'list->tail != list->head' to release all memory that should
> be released.
> 
> Fixes: a5623a203cff ("HID: hidraw: fix memory leak in hidraw_release()")
> Signed-off-by: Su Hui <suhui@nfschina.com>

This is very clever.  How did you find that?  Was it through static
analysis or just review?  Perhaps using syzkaller?

Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>

I imagine we could write a checker heuristic to identify ->tail and
->head struct members and then complain if they were ever used in a <
or > comparison.

regards,
dan carpenter

On 2024/1/25 15:11, Dan Carpenter wrote:
> On Thu, Jan 25, 2024 at 02:32:26PM +0800, Su Hui wrote:
>> 'struct hidraw_list' is a circular queue whose head can be smaller than
>> tail. Using 'list->tail != list->head' to release all memory that should
>> be released.
>>
>> Fixes: a5623a203cff ("HID: hidraw: fix memory leak in hidraw_release()")
>> Signed-off-by: Su Hui <suhui@nfschina.com>
> This is very clever.  How did you find that?  Was it through static
> analysis or just review?  Perhaps using syzkaller?
Hi,

I just met this bug on a real machine and found this problem by 
reviewing the code.

>
> Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
>
> I imagine we could write a checker heuristic to identify ->tail and
> ->head struct members and then complain if they were ever used in a <
> or > comparison.

I can't agree any more, great idea!

Su Hui