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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] ext4: Fix rec_len verify error
Date:   Sat, 29 Jul 2023 14:13:57 +0800
Message-Id: <20230729061357.1702891-1-zhangshida@kylinos.cn>
MIME-Version: 1.0
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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 millon 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 blocksize 65536, i.e. 0x10000.

But it is not the same condition when blocksize equals to 4k.
when enough files are created, the fake_dirent->reclen will be 0x1000.
it equals to 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, a special condition
was introduced to handle it properly.

Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
 fs/ext4/namei.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 0caf6c730ce3..a422cff25216 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -458,6 +458,9 @@ static struct dx_countlimit *get_dx_countlimit(struct inode *inode,
 		    root->info_length != sizeof(struct dx_root_info))
 			return NULL;
 		count_offset = 32;
+	} else if ((EXT4_BLOCK_SIZE(inode->i_sb) == 65536)
+		&& (le16_to_cpu(dirent->rec_len) == 65535)) {
+		count_offset = 8;
 	} else
 		return NULL;
 
-- 
2.27.0