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.

Reported-by: syzbot+1ad8bac5af24d01e2cbd@syzkaller.appspotmail.com
Tested-by: syzbot+1ad8bac5af24d01e2cbd@syzkaller.appspotmail.com
Reviewed-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Fixes: c3defd99d58c ("ext4: treat stripe in block unit")
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://patch.msgid.link/3a493bb503c3598e25dcfbed2936bb2dff3fece7.1725002410.git.ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index adc5046fe9dd5a29a2aadeb4ab11e5d600175aa1..16a4ce704460e141cebba38b88513221ca16461e 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5178,6 +5178,18 @@ 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;
@@ -5287,13 +5299,7 @@ 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",
@@ -6457,6 +6463,15 @@ 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