CVE-2024-35784: 
Linux Kernel vulnerability analysis and mitigation

A deadlock vulnerability was discovered in the Linux kernel's BTRFS filesystem implementation (CVE-2024-35784). The issue exists in the fiemap and extent locking mechanism, where holding the extent lock for the entire range during fiemap operations could lead to a deadlock condition. This vulnerability affects Linux kernel versions up to (excluding) 6.6.24 and versions from 6.7 up to (excluding) 6.7.12, as well as 6.8 release candidates (rc1-rc5) (NVD).

The vulnerability occurs due to a locking issue where the extent lock is held for the entire duration of fiemap operations. When copying fiemap extent to user space, a page fault can occur, and if the process attempts to mkwrite into a memory-mapped range of the same file, it results in a deadlock. The issue has a CVSS v3.1 base score of 5.5 (Medium) with vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H. The vulnerability is classified as CWE-667 (Improper Locking) (NVD, Kernel Patch).

The vulnerability can cause system deadlocks when using BTRFS filesystem operations, specifically during fiemap operations that interact with memory-mapped files. This can lead to system availability issues, though it does not directly impact confidentiality or integrity (NVD).

The vulnerability requires local access and can be triggered through normal filesystem operations when using BTRFS. A test case has been developed to reproduce the deadlock condition consistently (Kernel Patch).

The issue has been fixed by modifying the extent locking behavior to not hold the lock for the entire duration of the fiemap operation. The fix maintains a lock only when searching delalloc to ensure a consistent view of delalloc at the time of checking the delalloc flag. Users should upgrade to Linux kernel version 6.6.24, 6.7.12, or later versions that include the fix (Kernel Patch).