2018-05-29 06:22:43

by Nick Desaulniers

Subject: [PATCH] ext4: prefer strlcpy to strncpy

Fixes a stringop-truncation warning from gcc-8.

Signed-off-by: Nick Desaulniers <[email protected]>
---
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

2018-05-30 02:01:40

by Nick Desaulniers

Subject: Re: [PATCH] ext4: prefer strlcpy to strncpy

On Mon, May 28, 2018 at 11:21 PM, Nick Desaulniers
<[email protected]> wrote:
> Fixes a stringop-truncation warning from gcc-8.
>
> Signed-off-by: Nick Desaulniers <[email protected]>
> ---
> 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.

2018-05-30 05:17:21

by Theodore Ts'o

Subject: Re: [PATCH] ext4: prefer strlcpy to strncpy

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 <[email protected]>

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