lkml.org 
[lkml]   [2021]   [Jun]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 3/3] drivers/base/core: refcount kobject and bus on device attribute read / store
On Mon, Jun 21, 2021 at 04:36:51PM -0700, Luis Chamberlain wrote:
> It's possible today to have a device attribute read or store
> race against device removal. When this happens there is a small
> chance that the derefence for the private data area of the driver
> is NULL.
>
> Let's consider the zram driver as an example. Its possible to run into
> a race where a sysfs knob is being used, we get preempted, and a zram
> device is removed before we complete use of the sysfs knob. This can happen
> for instance on block devices, where for instance the zram block devices
> just part of the private data of the block device.
>
> For instance this can happen in the following two situations
> as examples to illustrate this better:
>
> CPU 1 CPU 2
> destroy_devices
> ...
> compact_store()
> zram = dev_to_zram(dev);
> idr_for_each(zram_remove_cb
> zram_remove
> ...
> kfree(zram)
> down_read(&zram->init_lock);
>
> CPU 1 CPU 2
> hot_remove_store
> compact_store()
> zram = dev_to_zram(dev);
> zram_remove
> kfree(zram)
> down_read(&zram->init_lock);
>
> To ensure the private data pointer is valid we could use bdget() / bdput()
> in between access, however that would mean doing that in all sysfs
> reads/stores on the driver. Instead a generic solution for all drivers
> is to ensure the device kobject is still valid and also the bus, if
> a bus is present.
>
> This issue does not fix a known crash, however this race was
> spotted by Minchan Kim through code inspection upon code review
> of another zram patch.
>
> Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> ---
> drivers/base/base.h | 2 ++
> drivers/base/bus.c | 4 ++--
> drivers/base/core.c | 42 ++++++++++++++++++++++++++++++++++++++----
> 3 files changed, 42 insertions(+), 6 deletions(-)

Please make this an independent patch of the zram mess and I will be
glad to consider it for the driver core tree then.

thanks,

greg k-h

\
 
 \ /
  Last update: 2021-06-22 09:46    [W:0.160 / U:0.852 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site