CVE-2026-43299
Received Received - Intake
Assertion Failure in Btrfs Filesystem Repair

Publication date: 2026-05-08

Last updated on: 2026-05-08

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: btrfs: do not ASSERT() when the fs flips RO inside btrfs_repair_io_failure() [BUG] There is a bug report that when btrfs hits ENOSPC error in a critical path, btrfs flips RO (this part is expected, although the ENOSPC bug still needs to be addressed). The problem is after the RO flip, if there is a read repair pending, we can hit the ASSERT() inside btrfs_repair_io_failure() like the following: BTRFS info (device vdc): relocating block group 30408704 flags metadata|raid1 ------------[ cut here ]------------ BTRFS: Transaction aborted (error -28) WARNING: fs/btrfs/extent-tree.c:3235 at __btrfs_free_extent.isra.0+0x453/0xfd0, CPU#1: btrfs/383844 Modules linked in: kvm_intel kvm irqbypass [...] ---[ end trace 0000000000000000 ]--- BTRFS info (device vdc state EA): 2 enospc errors during balance BTRFS info (device vdc state EA): balance: ended with status: -30 BTRFS error (device vdc state EA): parent transid verify failed on logical 30556160 mirror 2 wanted 8 found 6 BTRFS error (device vdc state EA): bdev /dev/nvme0n1 errs: wr 0, rd 0, flush 0, corrupt 10, gen 0 [...] assertion failed: !(fs_info->sb->s_flags & SB_RDONLY) :: 0, in fs/btrfs/bio.c:938 ------------[ cut here ]------------ assertion failed: !(fs_info->sb->s_flags & SB_RDONLY) :: 0, in fs/btrfs/bio.c:938 kernel BUG at fs/btrfs/bio.c:938! Oops: invalid opcode: 0000 [#1] SMP NOPTI CPU: 0 UID: 0 PID: 868 Comm: kworker/u8:13 Tainted: G W N 6.19.0-rc6+ #4788 PREEMPT(full) Tainted: [W]=WARN, [N]=TEST Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014 Workqueue: btrfs-endio simple_end_io_work RIP: 0010:btrfs_repair_io_failure.cold+0xb2/0x120 RSP: 0000:ffffc90001d2bcf0 EFLAGS: 00010246 RAX: 0000000000000051 RBX: 0000000000001000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffffffff8305cf42 RDI: 00000000ffffffff RBP: 0000000000000002 R08: 00000000fffeffff R09: ffffffff837fa988 R10: ffffffff8327a9e0 R11: 6f69747265737361 R12: ffff88813018d310 R13: ffff888168b8a000 R14: ffffc90001d2bd90 R15: ffff88810a169000 FS: 0000000000000000(0000) GS:ffff8885e752c000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 ------------[ cut here ]------------ [CAUSE] The cause of -ENOSPC error during the test case btrfs/124 is still unknown, although it's known that we still have cases where metadata can be over-committed but can not be fulfilled correctly, thus if we hit such ENOSPC error inside a critical path, we have no choice but abort the current transaction. This will mark the fs read-only. The problem is inside the btrfs_repair_io_failure() path that we require the fs not to be mount read-only. This is normally fine, but if we are doing a read-repair meanwhile the fs flips RO due to a critical error, we can enter btrfs_repair_io_failure() with super block set to read-only, thus triggering the above crash. [FIX] Just replace the ASSERT() with a proper return if the fs is already read-only.
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Meta Information
Published
2026-05-08
Last Modified
2026-05-08
Generated
2026-05-09
AI Q&A
2026-05-08
EPSS Evaluated
N/A
NVD
CVE-2026-43299
EUVD
EUVD-2026-28569
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel 6.19.0-rc6+
Helpful Resources
Exploitability
CWE
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KEV
KEV Icon
CWE ID Description
CWE-UNKNOWN
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability exists in the Linux kernel's btrfs filesystem. When btrfs encounters an ENOSPC (no space left on device) error during a critical operation, it switches the filesystem to read-only mode as expected. However, if a read repair operation is pending at the same time, the system can hit an assertion failure inside the btrfs_repair_io_failure() function because it assumes the filesystem is not read-only. This causes a kernel crash (BUG). The root cause is that the code did not properly handle the case where the filesystem flips to read-only during a read repair, leading to an invalid assertion and system crash.


How can this vulnerability impact me? :

This vulnerability can cause the Linux system to crash unexpectedly when the btrfs filesystem encounters a critical ENOSPC error and attempts a read repair. The crash results from an assertion failure triggered by the filesystem switching to read-only mode during the repair process. This can lead to system instability, potential data loss, or downtime as the kernel encounters a BUG and halts operations.


How can this vulnerability be detected on my network or system? Can you suggest some commands?

This vulnerability can be detected by monitoring the system logs for specific error messages related to btrfs filesystem operations. Look for kernel messages indicating assertion failures or errors such as ENOSPC (No space left on device) and messages about the filesystem flipping to read-only mode.

  • Check kernel logs for assertion failures related to btrfs_repair_io_failure(), for example using: dmesg | grep -i btrfs
  • Look for ENOSPC errors and read-only filesystem flips in logs: dmesg | grep -E 'ENOSPC|read-only|btrfs'
  • Monitor system journal logs for btrfs errors: journalctl -k | grep btrfs

What immediate steps should I take to mitigate this vulnerability?

Immediate mitigation involves updating the Linux kernel to a version where this vulnerability is fixed, as the issue is resolved by replacing the ASSERT() with a proper return when the filesystem is already read-only.

Until the kernel is updated, monitor the filesystem for ENOSPC errors and avoid running operations that may trigger the btrfs repair path under low disk space conditions.

Ensure backups are up to date to prevent data loss in case the filesystem flips to read-only or crashes.


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