CVE-2024-26794: 
Linux Kernel vulnerability analysis and mitigation

CVE-2024-26794 is a vulnerability in the Linux kernel's btrfs file system that involves a race condition between ordered extent completion and fiemap operation. The issue was discovered in early 2024 and affects the btrfs file system implementation. The vulnerability occurs when fiemap is called without FIEMAP_FLAG_SYNC and there are ordered extents completing while btrfs_next_leaf() is called (Kernel Git).

The vulnerability stems from a race condition that occurs when the target extent range is not locked for the whole duration of the fiemap call. This was initially done to avoid a deadlock in scenarios where the fiemap buffer is a memory-mapped range of the same file. The race condition manifests when a fiemap task processes a file extent item covering a specific range (e.g., [512K, 1M[) and an ordered extent completes for an overlapping range (e.g., [768K, 2M[]), resulting in the original extent being trimmed and a new extent being inserted. This can trigger a warning in emit_fiemap_extent() and cause fiemap to fail with -EINVAL (Kernel Git).

The vulnerability can cause the fiemap operation to fail with -EINVAL and trigger kernel warnings. While the use case that could trigger this issue is unlikely in practice, it can be triggered through fuzz testing. The vulnerability has been assigned a CVSS v3.1 base score of 5.3 (Medium) by CISA-ADP (NVD).

The vulnerability can be triggered when specific conditions are met, particularly during fuzz testing scenarios. While it represents a reliability issue, there is no indication of this vulnerability being actively exploited in the wild (Kernel Git).

The issue has been fixed in the Linux kernel through a patch that modifies the emit_fiemap_extent() function to handle three specific scenarios: adjusting the length of previously cached extents to prevent overlap, handling cases where file extent items match cached offsets, and managing situations where file extent items have smaller offsets than cached ones (Kernel Git).