Re: [PATCH net v2] net/mlx5: fix uaccess beyond "count" in debugfs read/write handlers

On Fri, Jul 06, 2018 at 10:18:09PM +0200, Jann Horn wrote:

In general, accessing userspace memory beyond the length of the supplied
buffer in VFS read/write handlers can lead to both kernel memory corruption
(via kernel_read()/kernel_write(), which can e.g. be triggered via
sys_splice()) and privilege escalation inside userspace.

In this case, the affected files are in debugfs (and should therefore only
be accessible to root) and check that *pos is zero (which prevents the
sys_splice() trick). Therefore, this is not a security fix, but rather a
small cleanup.

For the read handlers, fix it by using simple_read_from_buffer() instead of
custom logic.
For the write handler, add a check.

changed in v2:
 - also fix dbg_write()

Thanks Jann,

Next time, please don't put changelog in commit message.

Saeed, are you taking it to mlx5-next? It is cleanup and better to be
sent to -next.

Thanks,
Reviewed-by: Leon Romanovsky <redacted>