Re: [PATCH v2 1/2] coredump: use from_kuid/kgid when formatting corename

[ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman)]

Nicolas Iooss <nicolas.iooss_linux-oWGTIYur0i8@public.gmane.org> writes:

> When adding __printf attribute to cn_printf, gcc reports some issues:
>
>   fs/coredump.c:213:5: warning: format '%d' expects argument of type
>   'int', but argument 3 has type 'kuid_t' [-Wformat=]
>        err = cn_printf(cn, "%d", cred->uid);
>        ^
>   fs/coredump.c:217:5: warning: format '%d' expects argument of type
>   'int', but argument 3 has type 'kgid_t' [-Wformat=]
>        err = cn_printf(cn, "%d", cred->gid);
>        ^
>
> These warnings come from the fact that the value of uid/gid needs to be
> extracted from the kuid_t/kgid_t structure before being used as an
> integer.  More precisely, cred->uid and cred->gid need to be converted
> to either user-namespace uid/gid or to init_user_ns uid/gid.
>
> Use init_user_ns in order not to break existing ABI, and document this
> in Documentation/sysctl/kernel.txt.
>
> While at it, format uid and gid values with %u instead of %d because
> uid_t/__kernel_uid32_t and gid_t/__kernel_gid32_t are unsigned int.

Acked-by: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>

> Signed-off-by: Nicolas Iooss <nicolas.iooss_linux-oWGTIYur0i8@public.gmane.org>
> ---
>  Documentation/sysctl/kernel.txt | 4 ++--
>  fs/coredump.c                   | 8 ++++++--
>  2 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
> index c831001c45f1..e1913f78f21e 100644
> --- a/Documentation/sysctl/kernel.txt
> +++ b/Documentation/sysctl/kernel.txt
> @@ -197,8 +197,8 @@ core_pattern is used to specify a core dumpfile pattern name.
>  	%P	global pid (init PID namespace)
>  	%i	tid
>  	%I	global tid (init PID namespace)
> -	%u	uid
> -	%g	gid
> +	%u	uid (in initial user namespace)
> +	%g	gid (in initial user namespace)
>  	%d	dump mode, matches PR_SET_DUMPABLE and
>  		/proc/sys/fs/suid_dumpable
>  	%s	signal number
> diff --git a/fs/coredump.c b/fs/coredump.c
> index bbbe139ab280..833a57bc856c 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -209,11 +209,15 @@ static int format_corename(struct core_name *cn, struct coredump_params *cprm)
>  				break;
>  			/* uid */
>  			case 'u':
> -				err = cn_printf(cn, "%d", cred->uid);
> +				err = cn_printf(cn, "%u",
> +						from_kuid(&init_user_ns,
> +							  cred->uid));
>  				break;
>  			/* gid */
>  			case 'g':
> -				err = cn_printf(cn, "%d", cred->gid);
> +				err = cn_printf(cn, "%u",
> +						from_kgid(&init_user_ns,
> +							  cred->gid));
>  				break;
>  			case 'd':
>  				err = cn_printf(cn, "%d",