[PATCH] ext4: prefer strlcpy to strncpy

[PATCH] ext4: prefer strlcpy to strncpy

[Nick Desaulniers]

Fixes a stringop-truncation warning from gcc-8.

Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>
---
 fs/ext4/super.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index eb104e8..d47c85f 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -323,11 +323,11 @@ static void __save_error_info(struct super_block *sb, const char *func,
 		return;
 	es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
 	es->s_last_error_time = cpu_to_le32(get_seconds());
-	strncpy(es->s_last_error_func, func, sizeof(es->s_last_error_func));
+	strlcpy(es->s_last_error_func, func, sizeof(es->s_last_error_func));
 	es->s_last_error_line = cpu_to_le32(line);
 	if (!es->s_first_error_time) {
 		es->s_first_error_time = es->s_last_error_time;
-		strncpy(es->s_first_error_func, func,
+		strlcpy(es->s_first_error_func, func,
 			sizeof(es->s_first_error_func));
 		es->s_first_error_line = cpu_to_le32(line);
 		es->s_first_error_ino = es->s_last_error_ino;
-- 
2.7.4

Re: [PATCH] ext4: prefer strlcpy to strncpy

[Nick Desaulniers]

On Mon, May 28, 2018 at 11:21 PM, Nick Desaulniers
<nick.desaulniers@gmail.com> wrote:
> Fixes a stringop-truncation warning from gcc-8.
>
> Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>
> ---
>  fs/ext4/super.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index eb104e8..d47c85f 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -323,11 +323,11 @@ static void __save_error_info(struct super_block *sb, const char *func,
>                 return;
>         es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
>         es->s_last_error_time = cpu_to_le32(get_seconds());
> -       strncpy(es->s_last_error_func, func, sizeof(es->s_last_error_func));
> +       strlcpy(es->s_last_error_func, func, sizeof(es->s_last_error_func));
>         es->s_last_error_line = cpu_to_le32(line);
>         if (!es->s_first_error_time) {
>                 es->s_first_error_time = es->s_last_error_time;
> -               strncpy(es->s_first_error_func, func,
> +               strlcpy(es->s_first_error_func, func,
>                         sizeof(es->s_first_error_func));
>                 es->s_first_error_line = cpu_to_le32(line);
>                 es->s_first_error_ino = es->s_last_error_ino;
> --
> 2.7.4
>

Eric points out this will leave the rest of dest uninitialized if size
is less than length of src.

Re: [PATCH] ext4: prefer strlcpy to strncpy

[Theodore Y. Ts'o]

On Mon, May 28, 2018 at 11:21:53PM -0700, Nick Desaulniers wrote:
> Fixes a stringop-truncation warning from gcc-8.
> 
> Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>

I'll note that the ext4 superblock fields are *not* guaranteed to be
NULL terminated.  Code that references them must, and do, deal with
this appropriately.  See for example:

https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git/tree/lib/e2p/ls.c#n436

GCC-8 may whine about it, but the whine is, in fact, not correct.
It's making assumptions about all strings being null terminated, which
is often, but not always, the case.

Cheers,

						- Ted