[PATCH v3] ext4: Fix rec_len verify error

[zhangshida <starzhangzsd@gmail.com>]

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 files 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, helpers like ext4_rec_len_{from,to}_disk has already
been introduce to complete the conversion between the encoded and the
plain form of rec_len.

So fix this one by using the helper, and all the other
le16_to_cpu(ext4_dir_entry{,_2}.rec_len) accesses in this file too.

Cc: stable@kernel.org
Fixes: dbe89444042a ("ext4: Calculate and verify checksums for htree nodes")
Suggested-by: Andreas Dilger <adilger@dilger.ca>
Suggested-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
v1->v2:
 Use the existing helper to covert the rec_len, as suggested by Andreas.
v2->v3:
 1,Covert all the other rec_len if necessary, as suggested by Darrick.
 2,Rephrase the commit message.

 fs/ext4/namei.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 0caf6c730ce3..8cb377b8ad86 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -346,14 +346,14 @@ static struct ext4_dir_entry_tail *get_dirent_tail(struct inode *inode,
 
 #ifdef PARANOID
 	struct ext4_dir_entry *d, *top;
+	int blocksize = EXT4_BLOCK_SIZE(inode->i_sb);
 
 	d = (struct ext4_dir_entry *)bh->b_data;
 	top = (struct ext4_dir_entry *)(bh->b_data +
-		(EXT4_BLOCK_SIZE(inode->i_sb) -
-		 sizeof(struct ext4_dir_entry_tail)));
-	while (d < top && d->rec_len)
+		(blocksize - sizeof(struct ext4_dir_entry_tail)));
+	while (d < top && ext4_rec_len_from_disk(d->rec_len, blocksize))
 		d = (struct ext4_dir_entry *)(((void *)d) +
-		    le16_to_cpu(d->rec_len));
+		    ext4_rec_len_from_disk(d->rec_len, blocksize));
 
 	if (d != top)
 		return NULL;
@@ -445,13 +445,13 @@ 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) {
+	else if (ext4_rec_len_from_disk(dirent->rec_len, blocksize) == 12) {
 		dp = (struct ext4_dir_entry *)(((void *)dirent) + 12);
-		if (le16_to_cpu(dp->rec_len) !=
-		    EXT4_BLOCK_SIZE(inode->i_sb) - 12)
+		if (ext4_rec_len_from_disk(dp->rec_len, blocksize) != blocksize - 12)
 			return NULL;
 		root = (struct dx_root_info *)(((void *)dp + 12));
 		if (root->reserved_zero ||
-- 
2.27.0