CVE-2024-42304: ext4: make sure the first directory block is not a hole

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-08-17 · updated 2026-10-15

Description

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.

Affected products

Linux kernel: from 4.9.187 before 4.10; from 4.14.135 before 4.15; from 4.19.62 before 4.19.320; from 5.1.21 before 5.2; from 5.2.4 before 5.4.282; from 5.5 before 5.10.224 — fixed in 4.10, 4.15, 4.19.320, 5.10.224, 5.15.165, 5.2

How to fix

Upgrade to a fixed version: Linux kernel 4.10, 4.15, 4.19.320, 5.10.224. Check the vendor advisory for mitigations.

References

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