Linux kernel module: NULL pointer dereferences

[Didier Barvaux]

Mikhail Gruzdev reported on the mailing list that:

> The other thing I've noticed is that rohc_test throws multiple
> NULL-pointer dereference oopses in kernel log during the test.

And, in a follow-up message:

> > I didn't see them. What kernel version did you used?
>
> It's 3.2.0-23-generic-pae from ubuntu-12.04-desktop-i386 distribution.
> I've uploaded kernel and userspace message logs:
>
> https://docs.google.com/file/d/0B7kwArZeP9zXV256SjBabUY0TmM/edit?usp=sharing
>
> and
>
> https://docs.google.com/file/d/0B7kwArZeP9zXRTI1ZkpLUnBEb2s/edit?usp=sharing

[Didier Barvaux (didier-barvaux)]

The problem seems to be related to the way the ROHC compressor/decompressor couples are created and destroyed in the rohc_test.ko module. Upon the first /proc open, the couples are created. They are also released upon the first /proc close. However, some other /proc may still be used and ask the rohc_test.ko module to perform some compression/decompression.

Fix coded. To be tested in VM.