coredump: escape / in hostname and comm

Change every occurence of / in comm and hostname to !.  If the process
changes its name to contain /, the core is not dumped (if the directory
tree doesn't exist like that).  The same with hostname being something
like myhost/3.  Fix this behaviour by using the escape loop used in %E.
(We extract it to a separate function.)

Now both with comm == myprocess/1 and hostname == myhost/1, the core is
dumped like (kernel.core_pattern='core.%p.%e.%h):
core.2349.myprocess!1.myhost!1
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/exec.c

@@ -1649,15 +1649,26 @@ static int cn_printf(struct core_name *cn, const char *fmt, ...)
 	return ret;
 }
 
+static void cn_escape(char *str)
+{
+	for (; *str; str++)
+		if (*str == '/')
+			*str = '!';
+}
+
 static int cn_print_exe_file(struct core_name *cn)
 {
 	struct file *exe_file;
-	char *pathbuf, *path, *p;
+	char *pathbuf, *path;
 	int ret;
 
 	exe_file = get_mm_exe_file(current->mm);
-	if (!exe_file)
-		return cn_printf(cn, "%s (path unknown)", current->comm);
+	if (!exe_file) {
+		char *commstart = cn->corename + cn->used;
+		ret = cn_printf(cn, "%s (path unknown)", current->comm);
+		cn_escape(commstart);
+		return ret;
+	}
 
 	pathbuf = kmalloc(PATH_MAX, GFP_TEMPORARY);
 	if (!pathbuf) {
@@ -1671,9 +1682,7 @@ static int cn_print_exe_file(struct core_name *cn)
 		goto free_buf;
 	}
 
-	for (p = path; *p; p++)
-		if (*p == '/')
-			*p = '!';
+	cn_escape(path);
 
 	ret = cn_printf(cn, "%s", path);
 
@@ -1745,16 +1754,22 @@ static int format_corename(struct core_name *cn, long signr)
 				break;
 			}
 			/* hostname */
-			case 'h':
+			case 'h': {
+				char *namestart = cn->corename + cn->used;
 				down_read(&uts_sem);
 				err = cn_printf(cn, "%s",
 					      utsname()->nodename);
 				up_read(&uts_sem);
+				cn_escape(namestart);
 				break;
+			}
 			/* executable */
-			case 'e':
+			case 'e': {
+				char *commstart = cn->corename + cn->used;
 				err = cn_printf(cn, "%s", current->comm);
+				cn_escape(commstart);
 				break;
+			}
 			case 'E':
 				err = cn_print_exe_file(cn);
 				break;