Overview
CVE-2025-40244 describes an uninitialized value vulnerability discovered in the Linux kernel’s HFS+ file system implementation. Specifically, the issue resides within the __hfsplus_ext_cache_extent() function. This flaw could lead to unpredictable behavior and potential security implications if exploited. This issue was identified and reported by syzbot, a Linux kernel fuzzer, and has been addressed in recent kernel updates.
Technical Details
The vulnerability stems from the use of an uninitialized value within the __hfsplus_ext_cache_extent() function. The KMSAN (Kernel Memory Sanitizer) report highlighted the issue during file extension operations within the HFS+ file system. The specific call trace from the syzbot report is as follows:
[ 70.194323][ T9350] BUG: KMSAN: uninit-value in __hfsplus_ext_cache_extent+0x7d0/0x990
[ 70.195022][ T9350] __hfsplus_ext_cache_extent+0x7d0/0x990
[ 70.195530][ T9350] hfsplus_file_extend+0x74f/0x1cf0
[ 70.195998][ T9350] hfsplus_get_block+0xe16/0x17b0
[ 70.196458][ T9350] __block_write_begin_int+0x962/0x2ce0
[ 70.196959][ T9350] cont_write_begin+0x1000/0x1950
[ 70.197416][ T9350] hfsplus_write_begin+0x85/0x130
[ 70.197873][ T9350] generic_perform_write+0x3e8/0x1060
[ 70.198374][ T9350] __generic_file_write_iter+0x215/0x460
[ 70.198892][ T9350] generic_file_write_iter+0x109/0x5e0
[ 70.199393][ T9350] vfs_write+0xb0f/0x14e0
[ 70.199771][ T9350] ksys_write+0x23e/0x490
[ 70.200149][ T9350] __x64_sys_write+0x97/0xf0
[ 70.200570][ T9350] x64_sys_call+0x3015/0x3cf0
[ 70.201065][ T9350] do_syscall_64+0xd9/0x1d0
[ 70.201506][ T9350] entry_SYSCALL_64_after_hwframe+0x77/0x7f
The uninitialized value originates during memory allocation in the hfsplus_find_init function, which is called by hfsplus_file_extend. The allocated memory is then used without proper initialization, leading to the reported KMSAN error.
CVSS Analysis
Currently, a CVSS score is not available (N/A). The severity of this vulnerability is still being evaluated. However, uninitialized value vulnerabilities can potentially lead to information disclosure, denial-of-service, or other unpredictable behaviors. A CVSS score will likely be assigned as analysis progresses.
Possible Impact
While the exact impact depends on the specific usage of the uninitialized value, the potential consequences include:
- Information Leakage: The uninitialized memory might contain sensitive data from previous kernel operations, which could be exposed.
- Denial of Service (DoS): Using the uninitialized value could lead to crashes or unexpected behavior, causing a denial-of-service condition.
- Unpredictable Behavior: Depending on how the value is used, it could cause filesystem corruption or other unpredictable system states.
Mitigation and Patch Steps
The vulnerability has been addressed in the Linux kernel. The recommended mitigation is to update to a kernel version containing the fix. The specific commits that resolve the issue are listed in the references section below.
Users and administrators should apply the relevant kernel patches to their systems as soon as possible. Consider upgrading to a stable kernel release that includes the fix.
References
- Commit 1: 14c673a2f3ecf650b694a52a88688f1d71849899
- Commit 2: 4840ceadef4290c56cc422f0fc697655f3cbf070
- Commit 3: 99202d94909d323a30d154ab0261c0a07166daec
- Commit 4: a5bfb13b4f406aef1a450f99d22d3e48df01528c
- Commit 5: b8a72692aa42b7dcd179a96b90bc2763ac74576a
- Commit 6: c135b8dca65526aa5b8814e9954e0ae317d9c598
- Commit 7: c1ec90bed504640a42bb20a5f413be39cd17ad71
- Commit 8: d7e313039a8f3a6ee072dc5ff4643234d2d735cf
