Re: [PATCH] kdb: use sizeof(kdb_prompt_str) instead of mismatched CMD_BUFLEN

[David Laight <david.laight.linux@gmail.com>]

On Tue, 16 Jun 2026 22:14:54 +0530
Naveen Kumar Chaudhary <naveen.osdev@gmail.com> wrote:

> kdb_main.c defines CMD_BUFLEN as 200 (for command history buffers),
> while kdb_io.c defines it as 256 (for kdb_prompt_str). The snprintf()
> filling kdb_prompt_str incorrectly used the local CMD_BUFLEN (200),
> truncating the prompt unnecessarily. Use sizeof(kdb_prompt_str) to
> always match the actual buffer size.

As a matter of interest what sets the string that kdbgetenv("PROMPT")
returns?
If it is user settable, using it as a format string doesn't seem wise
(even for kdbg).

	David

> 
> Signed-off-by: Naveen Kumar Chaudhary <naveen.osdev@gmail.com>
> ---
>  kernel/debug/kdb/kdb_main.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
> index ddce56b47b25..571e9e61b40e 100644
> --- a/kernel/debug/kdb/kdb_main.c
> +++ b/kernel/debug/kdb/kdb_main.c
> @@ -1265,8 +1265,8 @@ static int kdb_local(kdb_reason_t reason, int error, struct pt_regs *regs,
>  
>  do_full_getstr:
>  		/* PROMPT can only be set if we have MEM_READ permission. */
> -		snprintf(kdb_prompt_str, CMD_BUFLEN, kdbgetenv("PROMPT"),
> -			 raw_smp_processor_id());
> +		snprintf(kdb_prompt_str, sizeof(kdb_prompt_str),
> +			 kdbgetenv("PROMPT"), raw_smp_processor_id());
>  
>  		/*
>  		 * Fetch command from keyboard