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ext4: make sure the first directory block is not a hole

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The syzbot constructs a directory that has no dirblock but is non-inline,
i.e. the first directory block is a hole. And no errors are reported when
creating files in this directory in the following flow.

    ext4_mknod
     ...
      ext4_add_entry
        // Read block 0
        ext4_read_dirblock(dir, block, DIRENT)
          bh = ext4_bread(NULL, inode, block, 0)
          if (!bh && (type == INDEX || type == DIRENT_HTREE))
          // The first directory block is a hole
          // But type == DIRENT, so no error is reported.

After that, we get a directory block without '.' and '..' but with a valid
dentry. This may cause some code that relies on dot or dotdot (such as
make_indexed_dir()) to crash.

Therefore when ext4_read_dirblock() finds that the first directory block
is a hole report that the filesystem is corrupted and return an error to
avoid loading corrupted data from disk causing something bad.

Reported-by: syzbot+ae688d469e36fb5138d0@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ae688d469e36fb5138d0
Fixes: 4e19d6b65f ("ext4: allow directory holes")
Cc: stable@kernel.org
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20240702132349.2600605-3-libaokun@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Baokun Li 2024-07-02 21:23:49 +08:00 committed by Theodore Ts'o
parent 50ea741def
commit f9ca51596b
1 changed files with 6 additions and 11 deletions
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17
fs/ext4/namei.c
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@ -151,10 +151,11 @@ static struct buffer_head *__ext4_read_dirblock(struct inode *inode,
return bh;
}
if (!bh && (type == INDEX || type == DIRENT_HTREE)) {
/* The first directory block must not be a hole. */
if (!bh && (type == INDEX || type == DIRENT_HTREE || block == 0)) {
ext4_error_inode(inode, func, line, block,
"Directory hole found for htree %s block",
(type == INDEX) ? "index" : "leaf");
"Directory hole found for htree %s block %u",
(type == INDEX) ? "index" : "leaf", block);
return ERR_PTR(-EFSCORRUPTED);
}
if (!bh)
@ -3129,10 +3130,7 @@ bool ext4_empty_dir(struct inode *inode)
EXT4_ERROR_INODE(inode, "invalid size");
return false;
}
/* The first directory block must not be a hole,
* so treat it as DIRENT_HTREE
*/
bh = ext4_read_dirblock(inode, 0, DIRENT_HTREE);
bh = ext4_read_dirblock(inode, 0, EITHER);
if (IS_ERR(bh))
return false;
@ -3577,10 +3575,7 @@ static struct buffer_head *ext4_get_first_dir_block(handle_t *handle,
struct ext4_dir_entry_2 *de;
unsigned int offset;
/* The first directory block must not be a hole, so
* treat it as DIRENT_HTREE
*/
bh = ext4_read_dirblock(inode, 0, DIRENT_HTREE);
bh = ext4_read_dirblock(inode, 0, EITHER);
if (IS_ERR(bh)) {
*retval = PTR_ERR(bh);
return NULL;