[PATCH RESENT] coredump: fix cn_printf formatting warnings

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

Add __printf attributes to cn_*printf functions.  With these, gcc says:

  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);
       ^
  fs/coredump.c:225:5: warning: format '%ld' expects argument of type
  'long int', but argument 3 has type 'int' [-Wformat=]
       err = cn_printf(cn, "%ld", cprm->siginfo->si_signo);
       ^

The third warning is easily fixed as si_signo is always an int.

For the two others, cred->uid and cred->gid need to be converted to
either a 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 current process namespace, it seems intuitive
that lowercase %u and %g use the current user namespace.  So implement
this.

Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
---

I sent this patch more than a month ago but go no feedback, so I'm sending it again.
Comments would be greatly appreciated.

 fs/coredump.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index bbbe139ab280..977fc8b91f2d 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -70,7 +70,8 @@ static int expand_corename(struct core_name *cn, int size)
 	return 0;
 }
 
-static int cn_vprintf(struct core_name *cn, const char *fmt, va_list arg)
+static __printf(2, 0) int cn_vprintf(struct core_name *cn, const char *fmt,
+				     va_list arg)
 {
 	int free, need;
 	va_list arg_copy;
@@ -93,7 +94,7 @@ again:
 	return -ENOMEM;
 }
 
-static int cn_printf(struct core_name *cn, const char *fmt, ...)
+static __printf(2, 3) int cn_printf(struct core_name *cn, const char *fmt, ...)
 {
 	va_list arg;
 	int ret;
@@ -105,7 +106,8 @@ static int cn_printf(struct core_name *cn, const char *fmt, ...)
 	return ret;
 }
 
-static int cn_esc_printf(struct core_name *cn, const char *fmt, ...)
+static __printf(2, 3)
+int cn_esc_printf(struct core_name *cn, const char *fmt, ...)
 {
 	int cur = cn->used;
 	va_list arg;
@@ -209,11 +211,15 @@ 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, "%d",
+						from_kuid_munged(cred->user_ns,
+								 cred->uid));
 				break;
 			/* gid */
 			case 'g':
-				err = cn_printf(cn, "%d", cred->gid);
+				err = cn_printf(cn, "%d",
+						from_kgid_munged(cred->user_ns,
+								 cred->gid));
 				break;
 			case 'd':
 				err = cn_printf(cn, "%d",
@@ -221,7 +227,7 @@ static int format_corename(struct core_name *cn, struct coredump_params *cprm)
 				break;
 			/* signal that caused the coredump */
 			case 's':
-				err = cn_printf(cn, "%ld", cprm->siginfo->si_signo);
+				err = cn_printf(cn, "%d", cprm->siginfo->si_signo);
 				break;
 			/* UNIX time of coredump */
 			case 't': {
-- 
2.3.5