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

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Message-ID: <957d29b85e06f415ee125de141809d2b9e084003.1723794770.git.ojaswin@linux.ibm.com>
Date: Fri, 16 Aug 2024 13:27:14 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>
Cc: Ritesh Harjani <ritesh.list@...il.com>, linux-kernel@...r.kernel.org,
        Kemeng Shi <shikemeng@...weicloud.com>,
        syzbot+1ad8bac5af24d01e2cbd@...kaller.appspotmail.com
Subject: [PATCH 1/2] ext4: Check stripe size compatibility on remount as well

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.

Additionally, change the users of EXT4_B2C(sbi->s_stripe) to
EXT4_NUM_B2C() so that if we ever accidentally hit this again, we can
avoid the value becoming 0. This should not change existing functionality.

Reported-by: syzbot+1ad8bac5af24d01e2cbd@...kaller.appspotmail.com
Tested-by: syzbot+1ad8bac5af24d01e2cbd@...kaller.appspotmail.com
Fixes: c3defd99d58c ("ext4: treat stripe in block unit")
Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
---
 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 e72145c4ae5a..9d495d78d262 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5165,6 +5165,18 @@ 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 simpfy code and avoid
+ * stripe aligned allocation which will rarely successes.
+ */
+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;
@@ -5272,13 +5284,7 @@ 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",
@@ -6441,6 +6447,15 @@ 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