Re: [PATCH] zram: Fix buffer size passed to strlcpy()

From: Doug Anderson
Date: Wed Aug 02 2017 - 18:54:41 EST


On Fri, Jul 28, 2017 at 10:12 AM, Matthias Kaehlcke <mka@xxxxxxxxxxxx> wrote:
> comp_algorithm_store() passes the size of the source buffer to strlcpy()
> instead of the destination buffer size, fix this.

This was introduced in commit 415403be37e2 ("zram: use crypto api to
check alg availability"), but probably don't need a "Fixes" since
there's not really a bug (see below)

> Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
> ---
> drivers/block/zram/zram_drv.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 856d5dc02451..7d2ddffad361 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -327,7 +327,7 @@ static ssize_t comp_algorithm_store(struct device *dev,
> return -EBUSY;
> }
> - strlcpy(zram->compressor, compressor, sizeof(compressor));
> + strlcpy(zram->compressor, compressor, sizeof(zram->compressor));

As far as I can tell the two sizes are identical. In struct zram:

char compressor[CRYPTO_MAX_ALG_NAME];

Locally here:

char compressor[CRYPTO_MAX_ALG_NAME]; there is no bug per say unless there's a hidden "#undef".
...but your change does make it a little clearer, plus if someone ever
changed one of these arrays it would be safer. Thus:

Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx>

I suppose another option would be to define the local array based on
the size of the structure. AKA locally in the function:

char compressor[ARRAY_SIZE(zram->compressor)];

...if you did that you could replace the strlcpy() below with a simple
strcpy() since you'd be guaranteed that there's be enough space.
...but I'm probably overthinking it too much. ;-P