Add a mutex fixing a potential NULL pointer dereference in the pi433 driver.
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@owl.eu.com> --- 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[0] 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. Regards, Hugo [0] http://lists.kernelnewbies.org/pipermail/kernelnewbies/2018-June/019131.html -- Hugo Lefeuvre (hle) | www.owl.eu.com 4096/ 9C4F C8BF A4B0 8FC5 48EB 56B8 1962 765B B9A8 BACA