coredump: add support for %d=__get_dumpable() in core name

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.

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

Developed during a discussion with Denys Vlasenko.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Alex Kelly <alex.page.kelly@gmail.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Cong Wang <amwang@redhat.com>
Cc: Jiri Moskovcak <jmoskovc@redhat.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 9 insertions, 3 deletions

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 6d78841fd416..2907ba6c3607 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -181,6 +181,8 @@ core_pattern is used to specify a core dumpfile pattern name.
         %p      pid
         %u      uid
         %g      gid
+        %d      dump mode, matches PR_SET_DUMPABLE and
+                /proc/sys/fs/suid_dumpable
         %s      signal number
         %t      UNIX time of dump
         %h      hostname
diff --git a/fs/coredump.c b/fs/coredump.c
index c01aa7b9ab5d..4fce06fc3b56 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': {
@@ -515,7 +519,7 @@ 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;