fix a leak in replace_fd() users

replace_fd() began with "eats a reference, tries to insert into
descriptor table" semantics; at some point I'd switched it to
much saner current behaviour ("try to insert into descriptor
table, grabbing a new reference if inserted; caller should do
fput() in any case"), but forgot to update the callers.
Mea culpa...

[Spotted by Pavel Roskin, who has really weird system with pipe-fed
coredumps as part of what he considers a normal boot ;-)]
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

fs/coredump.c

@@ -450,11 +450,12 @@ static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
 
 	cp->file = files[1];
 
-	replace_fd(0, files[0], 0);
+	err = replace_fd(0, files[0], 0);
+	fput(files[0]);
 	/* and disallow core files too */
 	current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};
 
-	return 0;
+	return err;
 }
 
 void do_coredump(siginfo_t *siginfo, struct pt_regs *regs)

security/selinux/hooks.c

@@ -2132,18 +2132,14 @@ static inline void flush_unauthorized_files(const struct cred *cred,
 		return;
 
 	devnull = dentry_open(&selinux_null, O_RDWR, cred);
-	if (!IS_ERR(devnull)) {
+	if (IS_ERR(devnull))
+		devnull = NULL;
 	/* replace all the matching ones with this */
 	do {
-			replace_fd(n - 1, get_file(devnull), 0);
+		replace_fd(n - 1, devnull, 0);
 	} while ((n = iterate_fd(files, n, match_file, cred)) != 0);
+	if (devnull)
 		fput(devnull);
-	} else {
-		/* just close all the matching ones */
-		do {
-			replace_fd(n - 1, NULL, 0);
-		} while ((n = iterate_fd(files, n, match_file, cred)) != 0);
-	}
 }
 
 /*