FAILED: patch "[PATCH] ext4: fix use-after-free race in ext4_remount()'s error path" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Theodore Ts'o <[email protected]>
Date: Fri, 12 Oct 2018 09:28:09 -0400
Subject: [PATCH] ext4: fix use-after-free race in ext4_remount()'s error path

It's possible for ext4_show_quota_options() to try reading s_qf_names[i] while it is being modified by ext4_remount() --- most notably, in ext4_remount's error path when the original values of the quota file name gets restored.

index 86e1bacac757..12f90d48ba61 100644
@@ -1405,7 +1405,8 @@ struct ext4_sb_info {
 	u32 s_min_batch_time;
 	struct block_device *journal_bdev;
 #ifdef CONFIG_QUOTA
-	char *s_qf_names[EXT4_MAXQUOTAS];	/* Names of quota files with journalled quota */
+	/* Names of quota files with journalled quota */
+	char __rcu *s_qf_names[EXT4_MAXQUOTAS];
 	int s_jquota_fmt;			/* Format of quota to use */
 #endif
 	unsigned int s_want_extra_isize; /* New inodes should reserve # bytes */