Re: [PATCH] ext4: fix -Wstringop-truncation warnings

[Wenlin Kang]

On 2020/12/16 下午12:20, Theodore Y. Ts'o wrote:

[Please note this e-mail is from an EXTERNAL e-mail address]

On Thu, Nov 12, 2020 at 05:33:24PM +0800, Kang Wenlin wrote:

From: Wenlin Kang 

The strncpy() function may create a unterminated string,
use strscpy_pad() instead.

This fixes the following warning:

fs/ext4/super.c: In function '__save_error_info':
fs/ext4/super.c:349:2: warning: 'strncpy' specified bound 32 equals destination 
size [-Wstringop-truncation]
   strncpy(es->s_last_error_func, func, sizeof(es->s_last_error_func));
   ^~~
fs/ext4/super.c:353:3: warning: 'strncpy' specified bound 32 equals destination 
size [-Wstringop-truncation]
strncpy(es->s_first_error_func, func,
^
 sizeof(es->s_first_error_func));
 ~~~

What compiler are you using?  s_last_error_func is defined to not
necessarily be NUL terminated.  So strscpy_pad() is not a proper
replacement for strncpy() in this use case.



My compiler is gcc 8.2.0,  this is found in v4.18, and I see mainline 
codes is
using the same code too,  so sent this patch. But according to your 
instructions,
I just re-check the code, with "__nonstring" attribute, it seems it has 
fixed.

Thank for your explain.




 From Documentation/process/deprecated:

If a caller is using non-NUL-terminated strings, strncpy() can
still be used, but destinations should be marked with the `__nonstring
`_
attribute to avoid future compiler warnings.

s_{first,last}_error_func is properly annotated with __nonstring in
fs/ext4/ext4.h.

 - Ted



--
Thanks,
Wenlin Kang

Re: [PATCH] ext4: fix -Wstringop-truncation warnings

[Theodore Y. Ts'o]

On Thu, Nov 12, 2020 at 05:33:24PM +0800, Kang Wenlin wrote:
> From: Wenlin Kang 
> 
> The strncpy() function may create a unterminated string,
> use strscpy_pad() instead.
> 
> This fixes the following warning:
> 
> fs/ext4/super.c: In function '__save_error_info':
> fs/ext4/super.c:349:2: warning: 'strncpy' specified bound 32 equals 
> destination size [-Wstringop-truncation]
>   strncpy(es->s_last_error_func, func, sizeof(es->s_last_error_func));
>   ^~~
> fs/ext4/super.c:353:3: warning: 'strncpy' specified bound 32 equals 
> destination size [-Wstringop-truncation]
>strncpy(es->s_first_error_func, func,
>^
> sizeof(es->s_first_error_func));
> ~~~

What compiler are you using?  s_last_error_func is defined to not
necessarily be NUL terminated.  So strscpy_pad() is not a proper
replacement for strncpy() in this use case.

>From Documentation/process/deprecated:

   If a caller is using non-NUL-terminated strings, strncpy() can
   still be used, but destinations should be marked with the `__nonstring
   `_
   attribute to avoid future compiler warnings.

s_{first,last}_error_func is properly annotated with __nonstring in
fs/ext4/ext4.h.

- Ted

[PATCH] ext4: fix -Wstringop-truncation warnings

[Kang Wenlin]

From: Wenlin Kang 

The strncpy() function may create a unterminated string,
use strscpy_pad() instead.

This fixes the following warning:

fs/ext4/super.c: In function '__save_error_info':
fs/ext4/super.c:349:2: warning: 'strncpy' specified bound 32 equals destination 
size [-Wstringop-truncation]
  strncpy(es->s_last_error_func, func, sizeof(es->s_last_error_func));
  ^~~
fs/ext4/super.c:353:3: warning: 'strncpy' specified bound 32 equals destination 
size [-Wstringop-truncation]
   strncpy(es->s_first_error_func, func,
   ^
sizeof(es->s_first_error_func));
~~~

Signed-off-by: Wenlin Kang 
---
 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 c3b864588a0b..3ade6e1f7a4d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -446,7 +446,7 @@ static void __save_error_info(struct super_block *sb, int 
error,
return;
es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
ext4_update_tstamp(es, s_last_error_time);
-   strncpy(es->s_last_error_func, func, sizeof(es->s_last_error_func));
+   strscpy_pad(es->s_last_error_func, func, sizeof(es->s_last_error_func));
es->s_last_error_line = cpu_to_le32(line);
es->s_last_error_ino = cpu_to_le32(ino);
es->s_last_error_block = cpu_to_le64(block);
@@ -507,7 +507,7 @@ static void __save_error_info(struct super_block *sb, int 
error,
if (!es->s_first_error_time) {
es->s_first_error_time = es->s_last_error_time;
es->s_first_error_time_hi = es->s_last_error_time_hi;
-   strncpy(es->s_first_error_func, func,
+   strscpy_pad(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;
-- 
2.17.1