On 5/28/26 02:18, Dan Carpenter wrote:
On Wed, May 27, 2026 at 08:31:59PM -0400, Sean Anderson wrote:
On 5/25/26 03:16, Dan Carpenter wrote:
If the *ppos is non-zero then simple_write_to_buffer() will not
initialize the start of the buf[] buffer. It doesn't really make sense
to allow non-zero values for *ppos, so check for that at the start and
return -EINVAL.
non-zero ppos seems to be handled properly by simple_write_to_buffer.
It's not an overflow bug, it's an uninitialized variable bug.
The simple_write_to_buffer() is designed to handle partial writes so it
leaves the first "written" (scare quotes) part of the string as is. But
in this case, we can't handle a partial write and the first part of
buf[] is left uninitialized.
https://staticthinking.wordpress.com/2026/05/23/simple_write_to_buffer-is-complicated/
OK, that's a bit strange. Can you add this to the doc comment? I certainly
missed it when looking around for appropriate functions.
And I like the explicit copy_from_user variant better, especially since
we are setting the nul-terminator anyway.
Also this appears to be dead code since fops_zynqmp_dp_pattern is never
used.
It's of course used in zynqmp_dp_bridge_debugfs_init.
--Sean
