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

On Fri, 2018-07-06 at 22:18 +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()

Fixes: e126ba97dba9 ("mlx5: Add driver for Mellanox Connect-IB
adapters")
Signed-off-by: Jann Horn <jannh@google.com>

Applied to mlx5-next, Thanks!!