[PATCH] state: check return value of chown

[Daniel Golle]

On Sat, Jan 02, 2021 at 10:01:36PM +0800, yeholmes at outlook.com wrote:
> From: Ye Holmes <yeholmes at outlook.com>
> 
> Output warning in case changing the ownership of ubus' home
> directory has failed. Besides, this avoids treating unused
> result warning as error by GCC (with glibc-2.31, version 10.2):
> 
> procd-2020-12-12-7f12c89d/state.c: In function 'state_enter':
> procd-2020-12-12-7f12c89d/state.c:147:4: error: ignoring
>   return value of 'chown' declared with attribute
>   'warn_unused_result' [-Werror=unused-result]
>   147 |    chown(p->pw_dir, p->pw_uid, p->pw_gid);
>       |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Signed-off-by: Ye Holmes <yeholmes at outlook.com>
> ---
>  state.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/state.c b/state.c
> index 44f56c6..d68776f 100644
> --- a/state.c
> +++ b/state.c
> @@ -144,7 +144,8 @@ static void state_enter(void)
>  		if (p) {
>  			LOG("- ubus -\n");
>  			mkdir(p->pw_dir, 0755);
> -			chown(p->pw_dir, p->pw_uid, p->pw_gid);
> +			if (chown(p->pw_dir, p->pw_uid, p->pw_gid))
> +				fprintf(stderr, "Failed to change ownership for %s\n", p->pw_dir);

Please let's not have a custom error message for cases which
practically never occur. If we would really cover all that, around
80% of the size of executables like procd would be error messages.
Imho an assertion is the right thing to do here.

>  		} else {
>  			LOG("- ubus (running as root!) -\n");
>  		}
> -- 
> 2.25.1
> 
> 
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