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SubjectRe: [PATCH] ext4: fix -Wstringop-truncation warnings
On Thu, Nov 12, 2020 at 05:33:24PM +0800, Kang Wenlin wrote:
> From: Wenlin Kang <wenlin.kang@windriver.com>
>
> 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
<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

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