tree f2410aed6f9d4aaaf3d299d62fc5caae126a6080
parent 9e98c678c2d6ae3a17cb2de55d17f69dddaa231b
author Jann Horn <jannh@google.com> 1550526189 +0100
committer Michal Simek <michal.simek@xilinx.com> 1552913034 +0100

firmware: xilinx: fix debugfs write handler

 - Userspace wants to write a string with `len` bytes, not counting the
   terminating NULL, so we should allocate `len+1` bytes. It looks like the
   current code relied on having a nullbyte directly behind `kern_buff`,
   which happens to work reliably as long as `len` isn't one of the kmalloc
   size classes.
 - strncpy_from_user() is completely wrong here; userspace is giving us a
   (not necessarily null-terminated) buffer and its length.
   strncpy_from_user() is for cases in which we don't know the length.
 - Don't let broken userspace allocate arbitrarily big kmalloc allocations.

Just use memdup_user_nul(), which is designed precisely for things like
this.

Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: Jolly Shah <jolly.shah@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>