Linux Kernel up to 6.17.12/6.18.1 btrfs_clear_space_info_full allocation of resources

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5.4$0-$5k0.00

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.17.12/6.18.1. It has been rated as critical. Affected by this issue is the function btrfs_clear_space_info_full. Performing a manipulation results in allocation of resources. This vulnerability was named CVE-2025-68358. The attack needs to be approached within the local network. There is no available exploit. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.17.12/6.18.1. It has been classified as critical. This affects the function btrfs_clear_space_info_full. The manipulation with an unknown input leads to a allocation of resources vulnerability. CWE is classifying the issue as CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. The impact remains unknown. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix racy bitfield write in btrfs_clear_space_info_full() From the memory-barriers.txt document regarding memory barrier ordering guarantees: (*) These guarantees do not apply to bitfields, because compilers often generate code to modify these using non-atomic read-modify-write sequences. Do not attempt to use bitfields to synchronize parallel algorithms. (*) Even in cases where bitfields are protected by locks, all fields in a given bitfield must be protected by one lock. If two fields in a given bitfield are protected by different locks, the compiler's non-atomic read-modify-write sequences can cause an update to one field to corrupt the value of an adjacent field. btrfs_space_info has a bitfield sharing an underlying word consisting of the fields full, chunk_alloc, and flush: struct btrfs_space_info { struct btrfs_fs_info * fs_info; /* 0 8 */ struct btrfs_space_info * parent; /* 8 8 */ ... int clamp; /* 172 4 */ unsigned int full:1; /* 176: 0 4 */ unsigned int chunk_alloc:1; /* 176: 1 4 */ unsigned int flush:1; /* 176: 2 4 */ ... Therefore, to be safe from parallel read-modify-writes losing a write to one of the bitfield members protected by a lock, all writes to all the bitfields must use the lock. They almost universally do, except for btrfs_clear_space_info_full() which iterates over the space_infos and writes out found->full = 0 without a lock. Imagine that we have one thread completing a transaction in which we finished deleting a block_group and are thus calling btrfs_clear_space_info_full() while simultaneously the data reclaim ticket infrastructure is running do_async_reclaim_data_space(): T1 T2 btrfs_commit_transaction btrfs_clear_space_info_full data_sinfo->full = 0 READ: full:0, chunk_alloc:0, flush:1 do_async_reclaim_data_space(data_sinfo) spin_lock(&space_info->lock); if(list_empty(tickets)) space_info->flush = 0; READ: full: 0, chunk_alloc:0, flush:1 MOD/WRITE: full: 0, chunk_alloc:0, flush:0 spin_unlock(&space_info->lock); return; MOD/WRITE: full:0, chunk_alloc:0, flush:1 and now data_sinfo->flush is 1 but the reclaim worker has exited. This breaks the invariant that flush is 0 iff there is no work queued or running. Once this invariant is violated, future allocations that go into __reserve_bytes() will add tickets to space_info->tickets but will see space_info->flush is set to 1 and not queue the work. After this, they will block forever on the resulting ticket, as it is now impossible to kick the worker again. I also confirmed by looking at the assembly of the affected kernel that it is doing RMW operations. For example, to set the flush (3rd) bit to 0, the assembly is: andb $0xfb,0x60(%rbx) and similarly for setting the full (1st) bit to 0: andb $0xfe,-0x20(%rax) So I think this is really a bug on practical systems. I have observed a number of systems in this exact state, but am currently unable to reproduce it. Rather than leaving this footgun lying around for the future, take advantage of the fact that there is room in the struct anyway, and that it is already quite large and simply change the three bitfield members to bools. This avoids writes to space_info->full having any effect on ---truncated---

It is possible to read the advisory at git.kernel.org. This vulnerability is uniquely identified as CVE-2025-68358 since 12/16/2025. The attack needs to approached within the local network. Technical details of the vulnerability are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 279768 (Linux Distros Unpatched Vulnerability : CVE-2025-68358), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.17.13, 6.18.2 or 6.19-rc1 eliminates this vulnerability. Applying the patch 6f442808a86eef847ee10afa9e6459494ed85bb3/742b90eaf394f0018352c0e10dc89763b2dd5267/38e818718c5e04961eea0fa8feff3f100ce40408 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (279768) and CERT Bund (WID-SEC-2025-2920). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Affected

  • Open Source Linux Kernel

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.5
VulDB Meta Temp Score: 5.4

VulDB Base Score: 5.5
VulDB Temp Score: 5.3
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 5.5
NVD Vector: 🔒

CVSSv2info

AVACAuCIA
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Allocation of resources
CWE: CWE-770 / CWE-400 / CWE-404
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 279768
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2025-68358

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.17.13/6.18.2/6.19-rc1
Patch: 6f442808a86eef847ee10afa9e6459494ed85bb3/742b90eaf394f0018352c0e10dc89763b2dd5267/38e818718c5e04961eea0fa8feff3f100ce40408

Timelineinfo

12/16/2025 CVE reserved
12/24/2025 +8 days Advisory disclosed
12/24/2025 +0 days VulDB entry created
02/26/2026 +64 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-68358 (🔒)
GCVE (CVE): GCVE-0-2025-68358
GCVE (VulDB): GCVE-100-338163
CERT Bund: WID-SEC-2025-2920 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 12/24/2025 15:21
Updated: 02/26/2026 19:59
Changes: 12/24/2025 15:21 (58), 12/25/2025 13:15 (7), 12/29/2025 06:00 (2), 02/26/2026 19:59 (10)
Complete: 🔍
Cache ID: 216::103

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