Re: [PATCH 08/11] blktrace: convert strncpy() to strscpy_pad()

Arnd Bergmann
2024-04-08T18:05:35Z

On Thu, Mar 28, 2024, at 15:14, Steven Rostedt wrote:
> On Thu, 28 Mar 2024 15:04:52 +0100
>>
>> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
>> index d5d94510afd3..95a00160d465 100644
>> --- a/kernel/trace/blktrace.c
>> +++ b/kernel/trace/blktrace.c
>> @@ -524,8 +524,7 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
>> if (!buts->buf_size || !buts->buf_nr)
>> return -EINVAL;
>>
>> - strncpy(buts->name, name, BLKTRACE_BDEV_SIZE);
>> - buts->name[BLKTRACE_BDEV_SIZE - 1] = '\0';
>> + strscpy(buts->name, name, BLKTRACE_BDEV_SIZE);
>
> The commit message says "Using strscpy_pad()" but it doesn't do so in the
> patch.
>
> Rule 12 of debugging: "When the comment and the code do not match, they are
> probably both wrong"

Thanks for double-checking this, I had a hard time deciding which
one to use here and ended up with an obviously inconsistent version.

I've changed it now to strscpy_pad() for v2, which is the slightly
safer choice here. The non-padding version would still not leak
kernel data but would write back user-provided data after the
padding instead of always zeroing it.

Arnd