# CVE-2026-93255: linux: In the Linux kernel, the following vulnerability has been resolved:  btrfs: make sure EXTENT_BUFFER_READING is cleare...

CVE-2026-93255 is fixed in linux on 1 platform by DEBIAN-CVE-2026-93255 (version 7.2.6-1), released September 24, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-93255
- Priority: Routine
- CVSS: n/a
- EPSS: 0.0020
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 24, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:  btrfs: make sure EXTENT_BUFFER_READING is cleared under refs_lock  [FALSE ALERTS] There is a bug report that the warning inside invalidate_and_check_btree_folios() got triggered during btrfs/298:   BTRFS info (device sdd): first mount of filesystem f9bf732a-a19b-44b9-99a7-614ddff168e2  BTRFS info (device sdd): using crc32c checksum algorithm  BTRFS error (device sdd): failed to find fsid cb2fdb42-b638-4f2f-badd-4127467ba674 when attempting to open seed devices  BTRFS error (device sdd): failed to read chunk tree: -2  ------------[ cut here ]------------  WARNING: disk-io.c:3342 at invalidate_and_check_btree_folios+0x260/0x3c0 [btrfs], CPU#4: mount/125993  CPU: 4 UID: 0 PID: 125993 Comm: mount Tainted: G        W  OE       7.1.0-rc7-custom+ #1 PREEMPT(full)  Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20250812-19.fc42 08/12/2025  Call trace:   invalidate_and_check_btree_folios+0x260/0x3c0 [btrfs] (P)   open_ctree+0x1f50/0x23b0 [btrfs]   btrfs_get_tree+0x89c/0xc48 [btrfs]   vfs_get_tree+0x30/0x110   vfs_cmd_create+0x58/0xe8   __arm64_sys_fsconfig+0x39c/0x518   invoke_syscall.constprop.0+0x48/0x120   el0_svc_common.constprop.0+0x40/0xe8   do_el0_svc+0x24/0x38   el0_svc+0x50/0x310   el0t_64_sync_handler+0xa0/0xe8   el0t_64_sync+0x198/0x1a0  ---[ end trace 0000000000000000 ]---  BTRFS warning (device sdd): unable to release extent buffer 365985792 owner 3 gen 17 refs 3 flags 0x5  [CAUSE] In that invalidate_and_check_btree_folios() we wait for the eb to finish its read, then check if it's only held by us and the btree inode.  If not, then do a warning as it may be still held, and could cause problems.  But there is a small window where the check can lead to false alerts:      Thread A (Read endio)         |        Thread B (Unmount) ----------------------------------+-------------------------------------  end_bbio_meta_read()             |  | The eb has one extra ref held  |  | by the reader, and has         |  | EXTENT_BUFFER_READING flag set | invalidate_and_check_btree_folios()  |                                | |  |- clear_extent_buffer_reading() | |  |                                | |- wait_on_bit_io();  |                                | |  The EXTENT_BUFFER_READING flag is  |                                | |  cleared  |                                | |- if (refcount_read(eb->refs) > 2)  |                                |    The eb is held by the read, us  |                                |    and btree inode, thus it  |                                |    will trigger the warning  |- free_extent_buffer()          |  [FIX] Introduce a helper, free_extent_buffer_clear_reading().  If the new parameter, @clear_reading, is set, we will hold the spinlock at the beginning of free_extent_buffer_clear_reading() to make sure the EXTENT_BUFFER_READING flag is cleared inside the same critical section of decreasing refs.  Now free_extent_buffer() will just call free_extent_buffer_clear_reading() with @clear_reading set to false, so no behavior change.  But for end_bbio_meta_read(), it will not clear_extent_buffer_reading() directly, but pass @clear_reading as true.  Then inside invalidate_and_check_btree_folios(), hold the refs_lock before reading refs. So that we eliminate the race window completely.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 14 | 7.2.6-1 | [DEBIAN-CVE-2026-93255](https://patchblox.com/security/data/fix/linux/debian-cve-2026-93255.md) | Sep 24, 2026 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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