CVE-2022-49708 is a vulnerability in the Linux kernel's ext4 filesystem implementation, specifically within the ext4_mb_use_inode_pa function in the block allocator code. The issue manifests as a kernel BUG_ON triggered due to an invalid condition where the length of a block extent (ac->ac_b_ex.fe_len) becomes zero or negative. This occurs during the process of marking disk space as used in ext4_mb_mark_diskspace_used. The root cause relates to improper handling of block allocation requests when the requested size is smaller than or equal to EXT4_BLOCKS_PER_GROUP, leading to truncation and misalignment of the start and size parameters. This can cause the ext4_mb_new_preallocation and related functions to compute invalid extents, ultimately triggering a kernel panic (BUG_ON). The vulnerability can be reproduced using a sequence of commands involving creating a small ext4 filesystem image with specific block and group sizes, mounting it, and running a stress test (fsstress) that exercises file write and sync operations. The flaw affects multiple Linux kernel versions identified by specific commit hashes. Although no known exploits are reported in the wild, the vulnerability can cause a denial of service (system crash) due to kernel panic when triggered. The issue was reported by Hulk Robot and resolved by correcting the logic that calculates block allocation extents to ensure proper alignment and size validation. This vulnerability impacts the stability and availability of Linux systems using ext4 filesystems under certain workloads that trigger the faulty allocation path.

For European organizations, the impact of CVE-2022-49708 primarily concerns system availability and reliability. Linux is widely used across Europe in servers, cloud infrastructure, and embedded systems, with ext4 being one of the most common filesystems. A triggered kernel panic can cause unexpected system crashes, leading to downtime and potential data loss if unsaved data is present. This can disrupt critical services, especially in sectors relying on Linux-based infrastructure such as finance, telecommunications, healthcare, and public administration. While the vulnerability does not directly enable privilege escalation or data confidentiality breaches, the denial of service can be leveraged by attackers to disrupt operations or as part of a multi-stage attack. Systems running workloads that perform intensive file write and sync operations on ext4 filesystems are at higher risk. The absence of known exploits in the wild reduces immediate threat but does not eliminate risk, particularly in environments where attackers have local access or can induce the vulnerable conditions. Organizations relying on Linux kernel versions affected by this flaw must consider the operational impact of potential crashes and the cost of downtime.

European organizations should apply the following specific mitigations: 1) Update Linux kernels to versions where CVE-2022-49708 is patched, ensuring the ext4 block allocator logic is corrected. 2) For systems where immediate patching is not feasible, limit or avoid workloads that perform aggressive file synchronization and stress testing on ext4 filesystems, particularly those involving small block groups or customized block sizes. 3) Implement robust monitoring of kernel logs and system stability to detect early signs of ext4-related kernel panics. 4) Employ filesystem integrity checks and backups to minimize data loss risk in case of crashes. 5) For critical infrastructure, consider using alternative filesystems less affected by this issue or deploying kernel live patching solutions if supported. 6) Restrict local access to trusted users only, as exploitation requires triggering specific filesystem operations. 7) Engage with Linux distribution vendors for timely security updates and advisories related to ext4 vulnerabilities.