ext4: fix memory leak in ext4_fill_super

static int kthread(void *_create) will return -ENOMEM
or -EINTR in case of internal failure or
kthread_stop() call happens before threadfn call.

To prevent fancy error checking and make code
more straightforward we moved all cleanup code out
of kmmpd threadfn.

Also, dropped struct mmpd_data at all. Now struct super_block
is a threadfn data and struct buffer_head embedded into
struct ext4_sb_info.

Reported-by: syzbot+d9e482e303930fa4f6ff@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Link: https://lore.kernel.org/r/20210430185046.15742-1-paskripkin@gmail.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -1488,6 +1488,7 @@ struct ext4_sb_info {
 	struct kobject s_kobj;
 	struct completion s_kobj_unregister;
 	struct super_block *s_sb;
+	struct buffer_head *s_mmp_bh;
 
 	/* Journaling */
 	struct journal_s *s_journal;
@@ -3720,6 +3721,9 @@ extern struct ext4_io_end_vec *ext4_last_io_end_vec(ext4_io_end_t *io_end);
 /* mmp.c */
 extern int ext4_multi_mount_protect(struct super_block *, ext4_fsblk_t);
 
+/* mmp.c */
+extern void ext4_stop_mmpd(struct ext4_sb_info *sbi);
+
 /* verity.c */
 extern const struct fsverity_operations ext4_verityops;
 

fs/ext4/mmp.c

@@ -127,9 +127,9 @@ void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
  */
 static int kmmpd(void *data)
 {
-	struct super_block *sb = ((struct mmpd_data *) data)->sb;
-	struct buffer_head *bh = ((struct mmpd_data *) data)->bh;
+	struct super_block *sb = (struct super_block *) data;
 	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
+	struct buffer_head *bh = EXT4_SB(sb)->s_mmp_bh;
 	struct mmp_struct *mmp;
 	ext4_fsblk_t mmp_block;
 	u32 seq = 0;
@@ -245,12 +245,18 @@ static int kmmpd(void *data)
 	retval = write_mmp_block(sb, bh);
 
 exit_thread:
-	EXT4_SB(sb)->s_mmp_tsk = NULL;
-	kfree(data);
-	brelse(bh);
 	return retval;
 }
 
+void ext4_stop_mmpd(struct ext4_sb_info *sbi)
+{
+	if (sbi->s_mmp_tsk) {
+		kthread_stop(sbi->s_mmp_tsk);
+		brelse(sbi->s_mmp_bh);
+		sbi->s_mmp_tsk = NULL;
+	}
+}
+
 /*
  * Get a random new sequence number but make sure it is not greater than
  * EXT4_MMP_SEQ_MAX.
@@ -275,7 +281,6 @@ int ext4_multi_mount_protect(struct super_block *sb,
 	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
 	struct buffer_head *bh = NULL;
 	struct mmp_struct *mmp = NULL;
-	struct mmpd_data *mmpd_data;
 	u32 seq;
 	unsigned int mmp_check_interval = le16_to_cpu(es->s_mmp_update_interval);
 	unsigned int wait_time = 0;
@@ -364,24 +369,17 @@ int ext4_multi_mount_protect(struct super_block *sb,
 		goto failed;
 	}
 
-	mmpd_data = kmalloc(sizeof(*mmpd_data), GFP_KERNEL);
-	if (!mmpd_data) {
-		ext4_warning(sb, "not enough memory for mmpd_data");
-		goto failed;
-	}
-	mmpd_data->sb = sb;
-	mmpd_data->bh = bh;
+	EXT4_SB(sb)->s_mmp_bh = bh;
 
 	/*
 	 * Start a kernel thread to update the MMP block periodically.
 	 */
-	EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, mmpd_data, "kmmpd-%.*s",
+	EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, sb, "kmmpd-%.*s",
 					     (int)sizeof(mmp->mmp_bdevname),
 					     bdevname(bh->b_bdev,
 						      mmp->mmp_bdevname));
 	if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
 		EXT4_SB(sb)->s_mmp_tsk = NULL;
-		kfree(mmpd_data);
 		ext4_warning(sb, "Unable to create kmmpd thread for %s.",
 			     sb->s_id);
 		goto failed;

fs/ext4/super.c

@@ -1245,8 +1245,8 @@ static void ext4_put_super(struct super_block *sb)
 	ext4_xattr_destroy_cache(sbi->s_ea_block_cache);
 	sbi->s_ea_block_cache = NULL;
 
-	if (sbi->s_mmp_tsk)
-		kthread_stop(sbi->s_mmp_tsk);
+	ext4_stop_mmpd(sbi);
+
 	brelse(sbi->s_sbh);
 	sb->s_fs_info = NULL;
 	/*
@@ -5186,8 +5186,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 failed_mount3:
 	flush_work(&sbi->s_error_work);
 	del_timer_sync(&sbi->s_err_report);
-	if (sbi->s_mmp_tsk)
-		kthread_stop(sbi->s_mmp_tsk);
+	ext4_stop_mmpd(sbi);
 failed_mount2:
 	rcu_read_lock();
 	group_desc = rcu_dereference(sbi->s_group_desc);
@@ -5989,8 +5988,7 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
 				 */
 				ext4_mark_recovery_complete(sb, es);
 			}
-			if (sbi->s_mmp_tsk)
-				kthread_stop(sbi->s_mmp_tsk);
+			ext4_stop_mmpd(sbi);
 		} else {
 			/* Make sure we can mount this feature set readwrite */
 			if (ext4_has_feature_readonly(sb) ||