CVE-2023-53243 in Linux
Summary
by MITRE • 09/15/2025
In the Linux kernel, the following vulnerability has been resolved:
btrfs: add handling for RAID1C23/DUP to btrfs_reduce_alloc_profile
Callers of `btrfs_reduce_alloc_profile` expect it to return exactly one allocation profile flag, and failing to do so may ultimately result in a WARN_ON and remount-ro when allocating new blocks, like the below transaction abort on 6.1.
`btrfs_reduce_alloc_profile` has two ways of determining the profile, first it checks if a conversion balance is currently running and uses the profile we're converting to. If no balance is currently running, it returns the max-redundancy profile which at least one block in the selected block group has.
This works by simply checking each known allocation profile bit in redundancy order. However, `btrfs_reduce_alloc_profile` has not been updated as new flags have been added - first with the `DUP` profile and later with the RAID1C34 profiles.
Because of the way it checks, if we have blocks with different profiles and at least one is known, that profile will be selected. However, if none are known we may return a flag set with multiple allocation profiles set.
This is currently only possible when a balance from one of the three unhandled profiles to another of the unhandled profiles is canceled after allocating at least one block using the new profile.
In that case, a transaction abort like the below will occur and the filesystem will need to be mounted with -o skip_balance to get it mounted rw again (but the balance cannot be resumed without a similar abort).
[770.648] ------------[ cut here ]------------
[770.648] BTRFS: Transaction aborted (error -22)
[770.648] WARNING: CPU: 43 PID: 1159593 at fs/btrfs/extent-tree.c:4122 find_free_extent+0x1d94/0x1e00 [btrfs]
[770.648] CPU: 43 PID: 1159593 Comm: btrfs Tainted: G W 6.1.0-0.deb11.7-powerpc64le #1 Debian 6.1.20-2~bpo11+1a~test
[770.648] Hardware name: T2P9D01 REV 1.00 POWER9 0x4e1202 opal:skiboot-bc106a0 PowerNV
[770.648] NIP: c00800000f6784fc LR: c00800000f6784f8 CTR: c000000000d746c0
[770.648] REGS: c000200089afe9a0 TRAP: 0700 Tainted: G W (6.1.0-0.deb11.7-powerpc64le Debian 6.1.20-2~bpo11+1a~test)
[770.648] MSR: 9000000002029033 <SF,HV,VEC,EE,ME,IR,DR,RI,LE> CR: 28848282 XER: 20040000
[770.648] CFAR: c000000000135110 IRQMASK: 0
GPR00: c00800000f6784f8 c000200089afec40 c00800000f7ea800 0000000000000026 GPR04: 00000001004820c2 c000200089afea00 c000200089afe9f8 0000000000000027 GPR08: c000200ffbfe7f98 c000000002127f90 ffffffffffffffd8 0000000026d6a6e8 GPR12: 0000000028848282 c000200fff7f3800 5deadbeef0000122 c00000002269d000 GPR16: c0002008c7797c40 c000200089afef17 0000000000000000 0000000000000000 GPR20: 0000000000000000 0000000000000001 c000200008bc5a98 0000000000000001 GPR24: 0000000000000000 c0000003c73088d0 c000200089afef17 c000000016d3a800 GPR28: c0000003c7308800 c00000002269d000 ffffffffffffffea 0000000000000001 [770.648] NIP [c00800000f6784fc] find_free_extent+0x1d94/0x1e00 [btrfs]
[770.648] LR [c00800000f6784f8] find_free_extent+0x1d90/0x1e00 [btrfs]
[770.648] Call Trace:
[770.648] [c000200089afec40] [c00800000f6784f8] find_free_extent+0x1d90/0x1e00 [btrfs] (unreliable)
[770.648] [c000200089afed30] [c00800000f681398] btrfs_reserve_extent+0x1a0/0x2f0 [btrfs]
[770.648] [c000200089afeea0] [c00800000f681bf0] btrfs_alloc_tree_block+0x108/0x670 [btrfs]
[770.648] [c000200089afeff0] [c00800000f66bd68] __btrfs_cow_block+0x170/0x850 [btrfs]
[770.648] [c000200089aff100] [c00800000f66c58c] btrfs_cow_block+0x144/0x288 [btrfs]
[770.648] [c000200089aff1b0] [c00800000f67113c] btrfs_search_slot+0x6b4/0xcb0 [btrfs]
[770.648] [c000200089aff2a0] [c00800000f679f60] lookup_inline_extent_backref+0x128/0x7c0 [btrfs]
[770.648] [c000200089aff3b0] [c00800000f67b338] lookup_extent_backref+0x70/0x190 [btrfs]
[770.648] [c000200089aff470] [c00800000f67b54c] __btrfs_free_extent+0xf4/0x1490 [btrfs]
[770.648] [
---truncated---
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Analysis
by VulDB Data Team • 01/11/2026
The vulnerability described in CVE-2023-53243 resides within the BTRFS filesystem implementation of the Linux kernel, specifically in the function `btrfs_reduce_alloc_profile`. This function is responsible for determining the appropriate allocation profile during block allocation operations, particularly when a balance operation is in progress or when selecting the maximum redundancy profile from existing block groups. The flaw arises from incomplete handling of newer RAID profile flags, namely DUP and RAID1C34, which were introduced after the original implementation of `btrfs_reduce_alloc_profile` was written. The function's logic iterates through known allocation profile bits in redundancy order, but fails to account for these newer profile types, leading to potential incorrect profile selection.
When a balance operation is canceled after allocating blocks with one of the unhandled profiles, the function may return a flag set that includes multiple allocation profiles simultaneously. This violates the expected behavior where the function should return exactly one allocation profile flag, causing a WARN_ON condition and ultimately resulting in a transaction abort. The system responds by remounting the filesystem read-only, rendering it unusable for write operations until manually corrected with the `skip_balance` mount option. The vulnerability is particularly dangerous because it can lead to complete filesystem unavailability and data access interruption, especially in production environments where BTRFS is heavily utilized for storage management.
The technical execution of this vulnerability requires specific conditions to manifest, including an active balance operation involving one of the unhandled profiles, followed by cancellation of that balance after at least one block has been allocated using the new profile. This creates a state where the profile selection logic cannot properly determine a single, valid allocation profile, triggering the kernel's warning mechanism and subsequent filesystem remount. The impact is consistent across different kernel versions and architectures, as demonstrated by the powerpc64le system logs showing the transaction abort error -22 and the warning in `find_free_extent` function. This vulnerability directly relates to CWE-129 and CWE-131 in the Common Weakness Enumeration, which cover issues related to improper handling of input validation and incorrect handling of buffer sizes, respectively. From an ATT&CK perspective, this vulnerability maps to T1490 (Inhibit System Recovery) and T1070.004 (File Deletion), as it can lead to filesystem corruption and unavailability, potentially requiring system recovery procedures and data restoration efforts.
Mitigation strategies for CVE-2023-53243 include upgrading to a patched kernel version that properly handles the DUP and RAID1C34 profile flags within `btrfs_reduce_alloc_profile`. Administrators should also implement monitoring for transaction abort warnings and filesystem remount events in BTRFS environments, particularly during balance operations. The recommended approach involves careful planning of balance operations and ensuring that systems are running patched kernel versions before initiating complex balance scenarios. Additionally, implementing regular filesystem checks and maintaining backup procedures can help recover from potential filesystem corruption. System administrators should also consider temporarily disabling balance operations on affected systems until the kernel is updated, as the vulnerability only manifests during specific balance cancellation scenarios. The fix implemented in the patched kernel ensures that `btrfs_reduce_alloc_profile` properly handles all known allocation profile flags, preventing the scenario where multiple profile flags are returned and causing the system to maintain a consistent and predictable allocation profile selection behavior.