CVE-2026-98080
UnknownSummary
In the Linux kernel, a bug in the btrfs subsystem forces unnecessary reloc root creation during snapshot creation when qgroups (quota) are enabled. This triggers a kernel warning in lookup_inline_extent_backref and flips the filesystem to read-only mode. The issue is reproducible during balance/relocate operations on a btrfs filesystem with quota enabled.
Risk Assessment
Organizations using btrfs filesystems with quota (qgroup) enabled may experience sudden read-only remounts, causing data unavailability and service disruption. This can impact continuity of applications relying on the affected volume.
Recommendation
Update the Linux kernel to a version containing the fix for CVE-2026-98080. Until patched, consider disabling quota on btrfs filesystems where balance/relocate or snapshot operations are performed.
Other vulnerabilities in Linux kernel (btrfs)
See all- CVE-2026-93255Unknown
In the Linux kernel, a race condition exists in the btrfs subsystem between the thread finishing an extent buffer read and the thread unmounting the filesystem. The EXTENT_BUFFER_READING flag is not cleared within the same critical section as the reference count decrement, leading to false warnings in invalidate_and_check_btree_folios(). The fix introduces a helper free_extent_buffer_clear_reading() and synchronization on refs_lock.
- CVE-2026-90265Unknown
A deadlock exists in the Linux kernel's btrfs filesystem during file defragmentation when autodefrag is enabled. Defrag reserves delalloc space while holding dirty and locked folios plus the extent range lock, causing kernel tasks (btrfs-cleaner, writeback, metadata reclaim) to block each other.
- CVE-2026-93800Low risk· EPSS 5%
In the Linux kernel's btrfs subsystem, a use-after-free vulnerability exists related to relocation operations. When insert_dirty_subvol() fails, a root's reloc_root field remains pointing to a freed reloc root instead of being set to NULL, leading to a use-after-free or double free during filesystem unmount.
- CVE-2026-89772Low risk· EPSS 7%
A flaw was found in the Linux kernel btrfs subsystem where write-protection of folios during data writeback was lost. A code change replaced folio_clear_dirty_for_io() with a plain folio_test_dirty() check, allowing a process with an mmap-ed file to modify sectors while writeback is in progress. This can cause checksum corruption, lost writes, and data corruption for compressed or inline extents.
- CVE-2023-3111High
A use after free vulnerability was found in prepare_to_relocate in fs/btrfs/relocation.c in the Linux Kernel. This possible flaw can be triggered by calling btrfs_ioctl_balance() before calling btrfs_ioctl_defrag().
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: btrfs: do not force reloc root creation during qgroup_account_snapshot() [BUG] When running btrfs/252 with quota enabled through MKFS_OPTIONS="-O quota", it has a high chance to trigger the following kernel warning and flips the fs RO: BTRFS info (device dm-2): relocating block group 30408704 flags metadata|dup ------------[ cut here ]------------ WARNING: fs/btrfs/extent-tree.c:879 at lookup_inline_extent_backref+0x74b/0x960 [btrfs], CPU#4: btrfs/2173 CPU: 4 UID: 0 PID: 2173 Comm: btrfs Not tainted 7.2.0-rc6-custom+ #457 PREEMPT(full) 3adc6528fb66f7a55fe1095385818e742f200aab Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS unknown 02/02/2022 RIP: 0010:lookup_inline_extent_backref+0x74b/0x960 [btrfs] Call Trace: <TASK> insert_inline_extent_backref+0x7c/0x160 [btrfs 32f09462c54d9c922fca74a3e4866f4aa7737b72] __btrfs_inc_extent_ref+0xa9/0x270 [btrfs 32f09462c54d9c922fca74a3e4866f4aa7737b72] __btrfs_run_delayed_refs+0x4af/0x11c0 [btrfs 32f09462c54d9c922fca74a3e4866f4aa7737b72] btrfs_run_delayed_refs+0x9d/0xf0 [btrfs 32f09462c54d9c922fca74a3e4866f4aa7737b72] create_pending_snapshot+0x39d/0xf00 [btrfs 32f09462c54d9c922fca74a3e4866f4aa7737b72] create_pending_snapshots+0x9b/0xc0 [btrfs 32f09462c54d9c922fca74a3e4866f4aa7737b72] btrfs_commit_transaction+0x280/0xeb0 [btrfs 32f09462c54d9c922fca74a3e4866f4aa7737b72] prepare_to_relocate+0x147/0x200 [btrfs 32f09462c54d9c922fca74a3e4866f4aa7737b72] relocate_block_group+0x6b/0x5e0 [btrfs 32f09462c54d9c922fca74a3e4866f4aa7737b72] btrfs_relocate_block_group+0x92c/0x2380 [btrfs 32f09462c54d9c922fca74a3e4866f4aa7737b72] btrfs_relocate_chunk+0x3f/0x1a0 [btrfs 32f09462c54d9c922fca74a3e4866f4aa7737b72] btrfs_balance+0xa2c/0x19c0 [btrfs 32f09462c54d9c922fca74a3e4866f4aa7737b72] btrfs_ioctl+0x2839/0x2d30 [btrfs 32f09462c54d9c922fca74a3e4866f4aa7737b72] __x64_sys_ioctl+0x416/0x9a0 do_syscall_64+0xe1/0x790 entry_SYSCALL_64_after_hwframe+0x4b/0x53 </TASK> ---[ end trace 0000000000000000 ]--- BTRFS info (device dm-2): leaf 4593991680 gen 233 total ptrs 175 free space 5953 owner 2 BTRFS info (device dm-2): refs 3 lock_owner 2173 current 2173 item 0 key (166772736 METADATA_ITEM 1) itemoff 16250 itemsize 33 extent refs 1 gen 222 flags 2 ref#0: tree block backref root 266 [ Skip the tree dump ] item 174 key (263225344 METADATA_ITEM 0) itemoff 10328 itemsize 33 extent refs 1 gen 162 flags 258 ref#0: tree block backref root 267 BTRFS error (device dm-2): extent item not found for insert, bytenr 179847168 num_bytes 16384 parent 4594335744 root_objectid 273 owner 0 offset 0 BTRFS error (device dm-2): failed to run delayed ref for logical 179847168 num_bytes 16384 type 182 action 1 ref_mod 1: -117 [CAUSE] The above error is showing that there is a tree reference to a metadata extent that is no longer there. With "ref_verify" mount option (requires CONFIG_BTRFS_DEBUG), there is some extra debug output: BTRFS error (device dm-2): dumping block entry [180961280 16384], num_refs 0, metadata 1, from disk 0 BTRFS error (device dm-2): root entry 256, num_refs 18446744073709551615 BTRFS error (device dm-2): root entry 273, num_refs 18446744073709551615 BTRFS error (device dm-2): Ref action 3, root 273, ref_root 273, parent 0, owner 0, offset 0, num_refs 1 btrfs_force_cow_block+0x129/0x7d0 [btrfs] btrfs_cow_block+0x10a/0x250 [btrfs] btrfs_search_slot+0x5eb/0xf40 [btrfs] btrfs_insert_empty_items+0x3a/0x70 [btrfs] insert_with_overflow+0x53/0x130 [btrfs] btrfs_insert_dir_item+0x125/0x290 [btrfs] btrfs_add_link+0xaa/0x410 [btrfs] btrfs_rename+0x5ea/0xcd0 [btrfs] btrfs_rename2+0x28/0x60 [btrfs] vfs_rename+0x5b2/0xe10 filename_renameat2+0x244/0x430 __x64_sys_rename+0x48/0x70 do_syscall_64+0xe1/0x790 entry_SYSCALL_64_after_hwframe+0x4b/0x53 ---truncated---
Vulnerability data from NVD (NIST) · CISA KEV · EPSS