Re: [PATCH v2] staging: pi433: add mutex fixing concurrency issues.
From: Hugo Lefeuvre
Date: Thu Jun 07 2018 - 08:45:14 EST
> Add a mutex fixing a potential NULL pointer dereference in the pi433
> If pi433_release and pi433_ioctl are concurrently called,
> pi433_release might set filp->private_data to NULL while pi433_ioctl
> is still accessing it, leading to NULL pointer dereference. This issue
> might also affect pi433_write and pi433_read.
> The newly introduced mutex makes sure that instance data
> will not be modified simultaneously by pi433_release, pi433_write,
> pi433_read or pi433_ioctl.
> The mutex is stored in a newly introduced struct pi433_data, which
> wraps struct pi433_instance and its mutex.
> Make filp->private_data point to a struct pi433_data, allowing to
> acquire the lock before accessing the struct pi433_instance.
> Signed-off-by: Hugo Lefeuvre <hle@xxxxxxxxxx>
> Changes in v2:
> - Use mutex instead of rw semaphore.
> - Introduce struct pi433_data in order to allow functions to lock
> before dereferencing instance pointer.
> - Make filp->private_data point to a struct pi433_data.
> - Add missing braces.
After discussing this issue on the kernel newbies mailing list we
came to the conclusion that it is very unlikely that pi433_release and
pi433_ioctl would ever run concurrently in this case. This is also
true for read/write. Unless one can find a situation where this might
happen, I think we should not add this potentially unnecessary lock.
Hugo Lefeuvre (hle) | www.owl.eu.com
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