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From:   zhangshida <starzhangzsd@gmail.com>
To:     tytso@mit.edu, adilger.kernel@dilger.ca
Cc:     linux-kernel@vger.kernel.org, zhangshida@kylinos.cn,
        starzhangzsd@gmail.com
Subject: [PATCH v2] ext4: Fix rec_len verify error
Date:   Sun, 30 Jul 2023 10:44:09 +0800
Message-Id: <20230730024409.1738559-1-zhangshida@kylinos.cn>
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From: Shida Zhang <zhangshida@kylinos.cn>

With the configuration PAGE_SIZE 64k and filesystem blocksize 64k,
a problem occurred when more than 13 million files were directly created
under a directory:

EXT4-fs error (device xx): ext4_dx_csum_set:492: inode #xxxx: comm xxxxx: dir seems corrupt?  Run e2fsck -D.
EXT4-fs error (device xx): ext4_dx_csum_verify:463: inode #xxxx: comm xxxxx: dir seems corrupt?  Run e2fsck -D.
EXT4-fs error (device xx): dx_probe:856: inode #xxxx: block 8188: comm xxxxx: Directory index failed checksum

When enough files are created, the fake_dirent->reclen will be 0xffff.
it doesn't equal to the blocksize 65536, i.e. 0x10000.

But it is not the same condition when blocksize equals to 4k.
when enough file are created, the fake_dirent->reclen will be 0x1000.
it equals to the blocksize 4k, i.e. 0x1000.

The problem seems to be related to the limitation of the 16-bit field
when the blocksize is set to 64k. To address this, Modify the check so
as to handle it properly.

Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
v1->v2:
  Use a better way to check the condition, as suggested by Andreas.

 fs/ext4/namei.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 0caf6c730ce3..fffed95f8531 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -445,8 +445,9 @@ static struct dx_countlimit *get_dx_countlimit(struct inode *inode,
 	struct ext4_dir_entry *dp;
 	struct dx_root_info *root;
 	int count_offset;
+	int blocksize = EXT4_BLOCK_SIZE(inode->i_sb);
 
-	if (le16_to_cpu(dirent->rec_len) == EXT4_BLOCK_SIZE(inode->i_sb))
+	if (ext4_rec_len_from_disk(dirent->rec_len, blocksize) == blocksize)
 		count_offset = 8;
 	else if (le16_to_cpu(dirent->rec_len) == 12) {
 		dp = (struct ext4_dir_entry *)(((void *)dirent) + 12);
-- 
2.27.0