High · published August 17, 2024
In the Linux kernel, the following vulnerability has been resolved:
ext4: make sure the first directory block is not a hole
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.
| Product | Versions | Fixed in |
|---|---|---|
| linux/linux_kernel | ≥ 4.9.187, < 4.10 | 4.10 |
| linux/linux_kernel | ≥ 4.14.135, < 4.15 | 4.15 |
| linux/linux_kernel | ≥ 4.19.62, < 4.19.320 | 4.19.320 |
| linux/linux_kernel | ≥ 5.1.21, < 5.2 | 5.2 |
| linux/linux_kernel | ≥ 5.2.4, < 5.4.282 | 5.4.282 |
| linux/linux_kernel | ≥ 5.5, < 5.10.224 | 5.10.224 |
| linux/linux_kernel | ≥ 5.11, < 5.15.165 | 5.15.165 |
| linux/linux_kernel | ≥ 5.16, < 6.1.103 | 6.1.103 |
| linux/linux_kernel | ≥ 6.2, < 6.6.44 | 6.6.44 |
| linux/linux_kernel | ≥ 6.7, < 6.10.3 | 6.10.3 |