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 <wenlin.kang@xxxxxxxxxxxxx>
> >
> > 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
>     <https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html>`_
>     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