exec.c: fix coredump to pipe problem and obscure "security hole"

The patch checks for "|" in the pattern not the output and doesn't nail a
pid on to a piped name (as it is a program name not a file)

Also fixes a very very obscure security corner case. If you happen to have
decided on a core pattern that starts with the program name then the user
can run a program called "|myevilhack" as it stands. I doubt anyone does
this.

Signed-off-by: Alan Cox <[e-mail]>
Confirmed-by: Christopher S. Aker <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/exec.c

···
  * name into corename, which must have space for at least
  * CORENAME_MAX_SIZE bytes plus one byte for the zero terminator.
  */
-static void format_corename(char *corename, const char *pattern, long signr)
+static int format_corename(char *corename, const char *pattern, long signr)
 {
 	const char *pat_ptr = pattern;
 	char *out_ptr = corename;
 	char *const out_end = corename + CORENAME_MAX_SIZE;
 	int rc;
 	int pid_in_pattern = 0;
+	int ispipe = 0;
+
+	if (*pattern == '|')
+		ispipe = 1;
 
 	/* Repeat as long as we have more pattern to process and more output
 	   space */
···
 	 *
 	 * If core_pattern does not include a %p (as is the default)
 	 * and core_uses_pid is set, then .%pid will be appended to
-	 * the filename */
-	if (!pid_in_pattern
+	 * the filename. Do not do this for piped commands. */
+	if (!ispipe && !pid_in_pattern
             && (core_uses_pid || atomic_read(&current->mm->mm_users) != 1)) {
 		rc = snprintf(out_ptr, out_end - out_ptr,
 			      ".%d", current->tgid);
···
 			goto out;
 		out_ptr += rc;
 	}
-      out:
+out:
 	*out_ptr = 0;
+	return ispipe;
 }
 
 static void zap_process(struct task_struct *start)
···
 	 * uses lock_kernel()
 	 */
  	lock_kernel();
-	format_corename(corename, core_pattern, signr);
+	ispipe = format_corename(corename, core_pattern, signr);
 	unlock_kernel();
- 	if (corename[0] == '|') {
+ 	if (ispipe) {
 		/* SIGPIPE can happen, but it's just never processed */
  		if(call_usermodehelper_pipe(corename+1, NULL, NULL, &file)) {
  			printk(KERN_INFO "Core dump to %s pipe failed\n",
 			       corename);
  			goto fail_unlock;
  		}
-		ispipe = 1;
  	} else
  		file = filp_open(corename,
 				 O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,