[PATCH v2] coredump: Add %f for executable file name.

[Lepton Wu <ytht.net@gmail.com>]

The document reads "%e" should be executable file name while actually
it could be changed by things like pr_ctl PR_SET_NAME. We can't really
change the behavior of "%e" for now, so introduce a new "%f" for the
real executable file name.

Signed-off-by: Lepton Wu <ytht.net@gmail.com>
---
 Documentation/admin-guide/sysctl/kernel.rst |  3 ++-
 fs/coredump.c                               | 17 +++++++++++++----
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 83acf5025488..17cd96a54fc4 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -164,7 +164,8 @@ core_pattern
 	%s		signal number
 	%t		UNIX time of dump
 	%h		hostname
-	%e		executable filename (may be shortened)
+	%e		executable filename (may be shortened, could be changed by prctl etc)
+	%f      	executable filename
 	%E		executable path
 	%c		maximum size of core file by resource limit RLIMIT_CORE
 	%<OTHER>	both are dropped
diff --git a/fs/coredump.c b/fs/coredump.c
index 7237f07ff6be..76e7c10edfc0 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -153,10 +153,10 @@ int cn_esc_printf(struct core_name *cn, const char *fmt, ...)
 	return ret;
 }
 
-static int cn_print_exe_file(struct core_name *cn)
+static int cn_print_exe_file(struct core_name *cn, bool name_only)
 {
 	struct file *exe_file;
-	char *pathbuf, *path;
+	char *pathbuf, *path, *ptr;
 	int ret;
 
 	exe_file = get_mm_exe_file(current->mm);
@@ -175,6 +175,11 @@ static int cn_print_exe_file(struct core_name *cn)
 		goto free_buf;
 	}
 
+	if (name_only) {
+		ptr = strrchr(path, '/');
+		if (ptr)
+			path = ptr + 1;
+	}
 	ret = cn_esc_printf(cn, "%s", path);
 
 free_buf:
@@ -301,12 +306,16 @@ static int format_corename(struct core_name *cn, struct coredump_params *cprm,
 					      utsname()->nodename);
 				up_read(&uts_sem);
 				break;
-			/* executable */
+			/* executable, could be changed by prctl PR_SET_NAME etc */
 			case 'e':
 				err = cn_esc_printf(cn, "%s", current->comm);
 				break;
+			/* file name of executable */
+			case 'f':
+				err = cn_print_exe_file(cn, true);
+				break;
 			case 'E':
-				err = cn_print_exe_file(cn);
+				err = cn_print_exe_file(cn, false);
 				break;
 			/* core limit size */
 			case 'c':
-- 
2.27.0.212.ge8ba1cc988-goog