[PATCH] ubifs: fix snprintf() checking

[PATCH] ubifs: fix snprintf() checking

[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@oracle.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;
 	}
-- 
2.30.2

Re: [PATCH] ubifs: fix snprintf() checking

[Alexander Dahl]

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@oracle.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@thorsis.com>

Greets
Alex