[PATCH -mm] coredump: add support for %d=__get_dumpable() in core name

[Oleg Nesterov <oleg@redhat.com>]

https://bugzilla.redhat.com/show_bug.cgi?id=787135

Some coredump handlers want to create a core file in a way compatible
with standard behavior. Standard behavior with fs.suid_dumpable = 2
is to create core file with uid=gid=0. However, there was no way for
coredump handler to know that the process being dumped was suid'ed.

This patch adds the new %d specifier for format_corename() which
simply reports __get_dumpable(mm->flags), this is compatible with
/proc/sys/fs/suid_dumpable we already have.

By-discussion-with: Denys Vlasenko <vda.linux@googlemail.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 fs/coredump.c |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index 1935b4d..aad8715 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -149,7 +149,7 @@ put_exe_file:
  * name into corename, which must have space for at least
  * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
  */
-static int format_corename(struct core_name *cn, long signr)
+static int format_corename(struct core_name *cn, struct coredump_params *cprm)
 {
 	const struct cred *cred = current_cred();
 	const char *pat_ptr = core_pattern;
@@ -194,9 +194,13 @@ static int format_corename(struct core_name *cn, long signr)
 			case 'g':
 				err = cn_printf(cn, "%d", cred->gid);
 				break;
+			case 'd':
+				err = cn_printf(cn, "%d",
+					__get_dumpable(cprm->mm_flags));
+				break;
 			/* signal that caused the coredump */
 			case 's':
-				err = cn_printf(cn, "%ld", signr);
+				err = cn_printf(cn, "%ld", cprm->signr);
 				break;
 			/* UNIX time of coredump */
 			case 't': {
@@ -524,7 +528,7 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
 	 */
 	clear_thread_flag(TIF_SIGPENDING);
 
-	ispipe = format_corename(&cn, signr);
+	ispipe = format_corename(&cn, &cprm);
 
  	if (ispipe) {
 		int dump_count;
-- 
1.5.5.1