[PATCH] mtd: Use kasprintf() instead of fixed buffer formatting

[PATCH] mtd: Use kasprintf() instead of fixed buffer formatting

[Geert Uytterhoeven]

Using "%4.4X" in the calculation of the buffer size is misleading, as
the format string literal has no relation to the actual size needed.
Hence this is fragile w.r.t. future modification.

As this is not a hot path, fix this by replacing the formatting in a
fixed buffer by kasprintf().

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
Compile-tested only.

Interestingly, this decreases code size (by 16 resp. 24 bytes on arm32
resp. arm64).
---
 drivers/mtd/chips/gen_probe.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/chips/gen_probe.c b/drivers/mtd/chips/gen_probe.c
index 879bebf9d8b12038..837b04ab96a9c526 100644
--- a/drivers/mtd/chips/gen_probe.c
+++ b/drivers/mtd/chips/gen_probe.c
@@ -202,16 +202,19 @@ static inline struct mtd_info *cfi_cmdset_unknown(struct map_info *map,
 	struct cfi_private *cfi = map->fldrv_priv;
 	__u16 type = primary?cfi->cfiq->P_ID:cfi->cfiq->A_ID;
 #ifdef CONFIG_MODULES
-	char probename[sizeof("cfi_cmdset_%4.4X")];
 	cfi_cmdset_fn_t *probe_function;
+	char *probename;
 
-	sprintf(probename, "cfi_cmdset_%4.4X", type);
+	probename = kasprintf(GFP_KERNEL, "cfi_cmdset_%4.4X", type);
+	if (!probename)
+		return NULL;
 
 	probe_function = __symbol_get(probename);
 	if (!probe_function) {
 		request_module("cfi_cmdset_%4.4X", type);
 		probe_function = __symbol_get(probename);
 	}
+	kfree(probename);
 
 	if (probe_function) {
 		struct mtd_info *mtd;
-- 
2.17.1

Re: [PATCH] mtd: Use kasprintf() instead of fixed buffer formatting

[Boris Brezillon]

On Thu, 28 Jun 2018 10:20:11 +0200
Geert Uytterhoeven <geert+renesas@glider.be> wrote:

> Using "%4.4X" in the calculation of the buffer size is misleading, as
> the format string literal has no relation to the actual size needed.
> Hence this is fragile w.r.t. future modification.
> 
> As this is not a hot path, fix this by replacing the formatting in a
> fixed buffer by kasprintf().
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Applied.

Thanks,

Boris

> ---
> Compile-tested only.
> 
> Interestingly, this decreases code size (by 16 resp. 24 bytes on arm32
> resp. arm64).
> ---
>  drivers/mtd/chips/gen_probe.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/chips/gen_probe.c b/drivers/mtd/chips/gen_probe.c
> index 879bebf9d8b12038..837b04ab96a9c526 100644
> --- a/drivers/mtd/chips/gen_probe.c
> +++ b/drivers/mtd/chips/gen_probe.c
> @@ -202,16 +202,19 @@ static inline struct mtd_info *cfi_cmdset_unknown(struct map_info *map,
>  	struct cfi_private *cfi = map->fldrv_priv;
>  	__u16 type = primary?cfi->cfiq->P_ID:cfi->cfiq->A_ID;
>  #ifdef CONFIG_MODULES
> -	char probename[sizeof("cfi_cmdset_%4.4X")];
>  	cfi_cmdset_fn_t *probe_function;
> +	char *probename;
>  
> -	sprintf(probename, "cfi_cmdset_%4.4X", type);
> +	probename = kasprintf(GFP_KERNEL, "cfi_cmdset_%4.4X", type);
> +	if (!probename)
> +		return NULL;
>  
>  	probe_function = __symbol_get(probename);
>  	if (!probe_function) {
>  		request_module("cfi_cmdset_%4.4X", type);
>  		probe_function = __symbol_get(probename);
>  	}
> +	kfree(probename);
>  
>  	if (probe_function) {
>  		struct mtd_info *mtd;