[PATCH v3 1/2] ext4: Check stripe size compatibility on remount as well

[Ojaswin Mujoo]

We disable stripe size in __ext4_fill_super if it is not a multiple of
the cluster ratio however this check is missed when trying to remount.
This can leave us with cases where stripe < cluster_ratio after
remount:set making EXT4_B2C(sbi->s_stripe) become 0 that can cause some
unforeseen bugs like divide by 0.

Fix that by adding the check in remount path as well.

Reported-by: syzbot+1ad8bac5af24d01e2cbd@xxxxxxxxxxxxxxxxxxxxxxxxx
Tested-by: syzbot+1ad8bac5af24d01e2cbd@xxxxxxxxxxxxxxxxxxxxxxxxx
Reviewed-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
Fixes: c3defd99d58c ("ext4: treat stripe in block unit")
Signed-off-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
---
 fs/ext4/super.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 58423e6bf3d0..0ba9c4e8ec44 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5173,6 +5173,18 @@ static int ext4_block_group_meta_init(struct super_block *sb, int silent)
 	return 0;
 }
 
+/*
+ * It's hard to get stripe aligned blocks if stripe is not aligned with
+ * cluster, just disable stripe and alert user to simplify code and avoid
+ * stripe aligned allocation which will rarely succeed.
+ */
+static bool ext4_is_stripe_incompatible(struct super_block *sb, unsigned long stripe)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	return (stripe > 0 && sbi->s_cluster_ratio > 1 &&
+		stripe % sbi->s_cluster_ratio != 0);
+}
+
 static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 {
 	struct ext4_super_block *es = NULL;
@@ -5280,13 +5292,7 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 		goto failed_mount3;
 
 	sbi->s_stripe = ext4_get_stripe_size(sbi);
-	/*
-	 * It's hard to get stripe aligned blocks if stripe is not aligned with
-	 * cluster, just disable stripe and alert user to simpfy code and avoid
-	 * stripe aligned allocation which will rarely successes.
-	 */
-	if (sbi->s_stripe > 0 && sbi->s_cluster_ratio > 1 &&
-	    sbi->s_stripe % sbi->s_cluster_ratio != 0) {
+	if (ext4_is_stripe_incompatible(sb, sbi->s_stripe)) {
 		ext4_msg(sb, KERN_WARNING,
 			 "stripe (%lu) is not aligned with cluster size (%u), "
 			 "stripe is disabled",
@@ -6450,6 +6456,15 @@ static int __ext4_remount(struct fs_context *fc, struct super_block *sb)
 
 	}
 
+	if ((ctx->spec & EXT4_SPEC_s_stripe) &&
+	    ext4_is_stripe_incompatible(sb, ctx->s_stripe)) {
+		ext4_msg(sb, KERN_WARNING,
+			 "stripe (%lu) is not aligned with cluster size (%u), "
+			 "stripe is disabled",
+			 ctx->s_stripe, sbi->s_cluster_ratio);
+		ctx->s_stripe = 0;
+	}
+
 	/*
 	 * Changing the DIOREAD_NOLOCK or DELALLOC mount options may cause
 	 * two calls to ext4_should_dioread_nolock() to return inconsistent
-- 
2.43.5