Re: [PATCH] gpiolib: fix memory leak in gpiochip_setup_dev

[Kent Gibson <warthog618@gmail.com>]

On Wed, Nov 09, 2022 at 12:57:48AM +0800, Kent Gibson wrote:
> On Tue, Nov 08, 2022 at 07:53:24PM +0800, Zeng Heng wrote:
> > gcdev_register & gcdev_unregister call device_add & device_del to
> > request/release source. But in device_add, the dev->p allocated by
> > device_private_init is not released by device_del.
> > 
> > So when calling gcdev_unregister to release gdev, it needs put_device
> > to release dev in the following.
> > 
> > Otherwise, kmemleak would report memory leak such as below:
> > 
> > unreferenced object 0xffff88810b406400 (size 512):
> >   comm "python3", pid 1682, jiffies 4295346908 (age 24.090s)
> >   hex dump (first 32 bytes):
> >     00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00  .....N..........
> >     ff ff ff ff ff ff ff ff a0 5e 23 90 ff ff ff ff  .........^#.....
> >   backtrace:
> >     [<00000000a58ee5fe>] kmalloc_trace+0x22/0x110
> >     [<0000000045fe2058>] device_add+0xb34/0x1130
> >     [<00000000d778b45f>] cdev_device_add+0x83/0xe0
> >     [<0000000089f948ed>] gpiolib_cdev_register+0x73/0xa0
> >     [<00000000a3a8a316>] gpiochip_setup_dev+0x1c/0x70
> >     [<00000000787227b4>] gpiochip_add_data_with_key+0x10f6/0x1bf0
> >     [<000000009ac5742c>] devm_gpiochip_add_data_with_key+0x2e/0x80
> >     [<00000000bf2b23d9>] xra1403_probe+0x192/0x1b0 [gpio_xra1403]
> >     [<000000005b5ef2d4>] spi_probe+0xe1/0x140
> >     [<000000002b26f6f1>] really_probe+0x17c/0x3f0
> >     [<00000000dd2dad9c>] __driver_probe_device+0xe3/0x170
> >     [<000000005ca60d2a>] device_driver_attach+0x34/0x80
> >     [<00000000e9db90db>] bind_store+0x10b/0x1a0
> >     [<00000000e2650f8a>] drv_attr_store+0x49/0x70
> >     [<0000000080a80b2b>] sysfs_kf_write+0x8c/0xb0
> >     [<00000000a28b45b9>] kernfs_fop_write_iter+0x216/0x2e0
> > 
> > unreferenced object 0xffff888100de9800 (size 512):
> >   comm "python3", pid 264, jiffies 4294737615 (age 33.514s)
> >   hex dump (first 32 bytes):
> >     00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00  .....N..........
> >     ff ff ff ff ff ff ff ff a0 5e 63 a1 ff ff ff ff  .........^c.....
> >   backtrace:
> >     [<00000000bcc571d0>] kmalloc_trace+0x22/0x110
> >     [<00000000eeb06124>] device_add+0xb34/0x1130
> >     [<000000007e5cd2fd>] cdev_device_add+0x83/0xe0
> >     [<000000008f6bcd3a>] gpiolib_cdev_register+0x73/0xa0
> >     [<0000000012c93b24>] gpiochip_setup_dev+0x1c/0x70
> >     [<00000000a24b646a>] gpiochip_add_data_with_key+0x10f6/0x1bf0
> >     [<000000000c225212>] tpic2810_probe+0x16e/0x196 [gpio_tpic2810]
> >     [<00000000b52d04ff>] i2c_device_probe+0x651/0x680
> >     [<0000000058d3ff6b>] really_probe+0x17c/0x3f0
> >     [<00000000586f43d3>] __driver_probe_device+0xe3/0x170
> >     [<000000003f428602>] device_driver_attach+0x34/0x80
> >     [<0000000040e91a1b>] bind_store+0x10b/0x1a0
> >     [<00000000c1d990b9>] drv_attr_store+0x49/0x70
> >     [<00000000a23bfc22>] sysfs_kf_write+0x8c/0xb0
> >     [<00000000064e6572>] kernfs_fop_write_iter+0x216/0x2e0
> >     [<00000000026ce093>] vfs_write+0x658/0x810
> > 
> > Because at the point of gpiochip_setup_dev here, where dev.release
> > does not set yet, calling put_device would cause the warning of
> > no release function and double-free in the following fault handler
> > route (when kfree dev_name). So directly calling kfree to release
> > dev->p here in case of memory leak.
> > 
> > Fixes: 1f5eb8b17f02 ("gpiolib: fix sysfs when cdev is not selected")
> 
> I'm confused. You say "gcdev_register & gcdev_unregister call device_add
> & device_del" - which is only the case when CONFIG_GPIO_CDEV is not set.
> 
> But your trace shows CONFIG_GPIO_CDEV is set, as otherwise
> gpiolib_cdev_register() would not exist.
> 
> Can you clarify the configuration in which you are seeing the problem?
> 
> Assuming CONFIG_GPIO_CDEV is NOT set:
> 
> Provide a more appropriate trace.
> 
> From a reading of the device_add() documentation, there is a problem if
> the device_add() fails - in that case put_device() should be called - and
> it is not, instead gpiochip_setup_dev() returns immediately - not going
> via the err_remove_device path where your fix is??.
> The correct fix for that would be to change the gcdev_register() to call
> put_device() if device_add() fails.
> 

Ignore that - as you mentioned the dev.release hasn't been set at that
point.

Having another look at this, I don't think the problem is related to the
Fixed commit at all - it looks more general.
How did you conclude that that commit introduced the problem?
Is it easily repeatable and have you bisected for it?

Cheers,
Kent.