[PATCH 1/2] coredump: use from_kuid/kgid_munged when formatting corename

[Nicolas Iooss <nicolas.iooss_linux@m4x.org>]

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.

As Documentation/sysctl/kernel.txt does not specify which user namespace
is used to translate %u and %g in core_pattern, but lowercase %p and %i
are used to format pid/tid in the current process namespace, it seems
intuitive that lowercase %u and %g use the current user namespace.

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.

Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
---
 fs/coredump.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index bbbe139ab280..99c8af640c5a 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_munged(cred->user_ns,
+								 cred->uid));
 				break;
 			/* gid */
 			case 'g':
-				err = cn_printf(cn, "%d", cred->gid);
+				err = cn_printf(cn, "%u",
+						from_kgid_munged(cred->user_ns,
+								 cred->gid));
 				break;
 			case 'd':
 				err = cn_printf(cn, "%d",
-- 
2.3.6