Re: [PATCH] powerpc/pseries/lparcfg: size the scratch buffer to the system parameter payload

[R Nageswara Sastry <rnsastry@linux.ibm.com>]

On 01.04.2026 9:33 PM, Pengpeng Hou wrote:
> parse_system_parameter_string() reads the shared processor LPAR
> attributes into a firmware buffer that can hold up to 4000 bytes, but it
> still tokenizes that payload through a fixed 1026-byte scratch buffer. A
> single long key-value fragment can therefore overrun the local parser
> buffer before the next comma delimiter is seen.
>
> Allocate the scratch buffer to the current payload size so tokenization
> stays within bounds.
>
> Fixes: fff9846be00c ("powerpc/pseries/lparcfg: convert to papr_sysparm API")
> Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
> ---

Tested-by: R Nageswara Sastry <rnsastry@linux.ibm.com>

Tested with different sizes of the buffer namely 1000, 1026, 1500, 2000, 
3900, 4000, 1027, 3500 with a sample test kernel module. Using the same 
module injected the text with the above sizes in to lparcfg
Example:

system_potential_processors=8HIJKLMN...GHIJK

>   arch/powerpc/platforms/pseries/lparcfg.c | 23 +++++++++++++----------
>   1 file changed, 13 insertions(+), 10 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pseries/lparcfg.c b/arch/powerpc/platforms/pseries/lparcfg.c
> index 8821c378bfff..c09f474c241e 100644
> --- a/arch/powerpc/platforms/pseries/lparcfg.c
> +++ b/arch/powerpc/platforms/pseries/lparcfg.c
> @@ -385,8 +385,6 @@ static void read_lpar_name(struct seq_file *m)
>   		read_dt_lpar_name(m);
>   }
>   
> -#define SPLPAR_MAXLENGTH 1026*(sizeof(char))
> -
>   /*
>    * parse_system_parameter_string()
>    * Retrieve the potential_processors, max_entitled_capacity and friends
> @@ -407,27 +405,32 @@ static void parse_system_parameter_string(struct seq_file *m)
>   		const char *local_buffer;
>   		int splpar_strlen;
>   		int idx, w_idx;
> -		char *workbuffer = kzalloc(SPLPAR_MAXLENGTH, GFP_KERNEL);
> -
> -		if (!workbuffer)
> -			goto out_free;
> +		size_t workbuf_size;
> +		char *workbuffer;
>   
>   		splpar_strlen = be16_to_cpu(buf->len);
>   		local_buffer = buf->val;
> +		workbuf_size = splpar_strlen + 1;
> +
> +		workbuffer = kzalloc(workbuf_size, GFP_KERNEL);
> +		if (!workbuffer)
> +			goto out_free;
>   
>   		w_idx = 0;
>   		idx = 0;
> -		while ((*local_buffer) && (idx < splpar_strlen)) {
> +		while ((idx < splpar_strlen) && local_buffer[idx]) {
>   			workbuffer[w_idx++] = local_buffer[idx++];
> -			if ((local_buffer[idx] == ',')
> +			if (idx >= splpar_strlen ||
> +			    (local_buffer[idx] == ',')
>   			    || (local_buffer[idx] == '\0')) {
>   				workbuffer[w_idx] = '\0';
>   				if (w_idx) {
>   					/* avoid the empty string */
>   					seq_printf(m, "%s\n", workbuffer);
>   				}
> -				memset(workbuffer, 0, SPLPAR_MAXLENGTH);
> -				idx++;	/* skip the comma */
> +				memset(workbuffer, 0, workbuf_size);
> +				if (idx < splpar_strlen)
> +					idx++;	/* skip the comma */
>   				w_idx = 0;
>   			} else if (local_buffer[idx] == '=') {
>   				/* code here to replace workbuffer contents

-- 
Thanks and Regards
R.Nageswara Sastry