linux-kernel - Re: [PATCH] ubifs: fix snprintf() checking

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Date:   Wed, 12 May 2021 10:22:22 +0200
From:   Alexander Dahl <ada@...rsis.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Richard Weinberger <richard@....at>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Artem Bityutskiy <Artem.Bityutskiy@...ia.com>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] ubifs: fix snprintf() checking

Hello,

Am Tue, May 11, 2021 at 10:12:00AM +0300 schrieb Dan Carpenter:
> The snprintf() function returns the number of characters (not
> counting the NUL terminator) that it would have printed if we
> had space.
> 
> This buffer has UBIFS_DFS_DIR_LEN characters plus one extra for
> the terminator.  Printing UBIFS_DFS_DIR_LEN is okay but anything
> higher will result in truncation.  Thus the comparison needs to be
> change from == to >.
> 
> These strings are compile time constants so this patch doesn't
> affect runtime.
> 
> Fixes: ae380ce04731 ("UBIFS: lessen the size of debugging info data structure")
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
>  drivers/mtd/ubi/debug.c | 2 +-
>  fs/ubifs/debug.c        | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/ubi/debug.c b/drivers/mtd/ubi/debug.c
> index ac2bdba8bb1a..3c0c8eca4d51 100644
> --- a/drivers/mtd/ubi/debug.c
> +++ b/drivers/mtd/ubi/debug.c
> @@ -511,7 +511,7 @@ int ubi_debugfs_init_dev(struct ubi_device *ubi)
>  
>  	n = snprintf(d->dfs_dir_name, UBI_DFS_DIR_LEN + 1, UBI_DFS_DIR_NAME,
>  		     ubi->ubi_num);
> -	if (n == UBI_DFS_DIR_LEN) {
> +	if (n > UBI_DFS_DIR_LEN) {
>  		/* The array size is too small */
>  		return -EINVAL;
>  	}
> diff --git a/fs/ubifs/debug.c b/fs/ubifs/debug.c
> index 1bbb9fe661b1..fc718f6178f2 100644
> --- a/fs/ubifs/debug.c
> +++ b/fs/ubifs/debug.c
> @@ -2824,7 +2824,7 @@ void dbg_debugfs_init_fs(struct ubifs_info *c)
>  
>  	n = snprintf(d->dfs_dir_name, UBIFS_DFS_DIR_LEN + 1, UBIFS_DFS_DIR_NAME,
>  		     c->vi.ubi_num, c->vi.vol_id);
> -	if (n == UBIFS_DFS_DIR_LEN) {
> +	if (n > UBIFS_DFS_DIR_LEN) {
>  		/* The array size is too small */
>  		return;
>  	}

Reviewed-by: Alexander Dahl <ada@...rsis.com>

Greets
Alex