Re: [PATCH] printk: ringbuffer: Fix truncating buffer size min_t cast

[Vijay Balakrishna]

On 8/10/23 22:45, Kees Cook wrote:
> If an output buffer size exceeded U16_MAX, the min_t(u16, ...) cast in
> copy_data() was causing writes to truncate. This manifested as output
> bytes being skipped, seen as %NUL bytes in pstore dumps when the available
> record size was larger than 65536. Fix the cast to no longer truncate
> the calculation.
> 
> Cc: Petr Mladek <pmladek@xxxxxxxx>
> Cc: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: John Ogness <john.ogness@xxxxxxxxxxxxx>
> Reported-by: Vijay Balakrishna <vijayb@xxxxxxxxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/lkml/d8bb1ec7-a4c5-43a2-9de0-9643a70b899f@xxxxxxxxxxxxxxxxxxx/
> Fixes: b6cf8b3f3312 ("printk: add lockless ringbuffer")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Excellent.

I have verified on v5.10.

Tested-by: Vijay Balakrishna <vijayb@xxxxxxxxxxxxxxxxxxx>

Thanks,
Vijay