CVE-2026-23230: smb: client: split cached_fid bitfields to avoid shared-byte RMW races

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-02-18 · updated 2026-10-19
Weakness: CWE-362

Description

In the Linux kernel, the following vulnerability has been resolved: smb: client: split cached_fid bitfields to avoid shared-byte RMW races is_open, has_lease and on_list are stored in the same bitfield byte in struct cached_fid but are updated in different code paths that may run concurrently. Bitfield assignments generate byte read–modify–write operations (e.g. `orb $mask, addr` on x86_64), so updating one flag can restore stale values of the others. A possible interleaving is: CPU1: load old byte (has_lease=1, on_list=1) CPU2: clear both flags (store 0) CPU1: RMW store (old | IS_OPEN) -> reintroduces cleared bits To avoid this class of races, convert these flags to separate bool fields.

Affected products

Linux kernel: from 6.1 before 6.1.164; from 6.2 before 6.6.125; from 6.7 before 6.12.72; from 6.13 before 6.18.11; from 6.19 before 6.19.1 — fixed in 6.1.164, 6.12.72, 6.18.11, 6.19.1, 6.6.125

How to fix

Upgrade to a fixed version: Linux kernel 6.1.164, 6.12.72, 6.18.11, 6.19.1. Check the vendor advisory for mitigations.

References

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