CVE-2026-52906 - 9p: fix access mode flags being ORed instead of replaced

CVE-2026-52906 - 9p: fix access mode flags being ORed instead of replaced

https://cvefeed.io/rssfeed/latest.atom / Tue, 06/09/2026 - 17:28
CVE ID :CVE-2026-52906
Published : June 9, 2026, 2:16 p.m. | 48 minutes ago
Description :In the Linux kernel, the following vulnerability has been resolved: 9p: fix access mode flags being ORed instead of replaced Since commit 1f3e4142c0eb ("9p: convert to the new mount API"), v9fs_apply_options() applies parsed mount flags with |= onto flags already set by v9fs_session_init(). For 9P2000.L, session_init sets V9FS_ACCESS_CLIENT as the default, so when the user mounts with "access=user", both bits end up set. Access mode checks compare against exact values, so having both bits set matches neither mode. This causes v9fs_fid_lookup() to fall through to the default switch case, using INVALID_UID (nobody/65534) instead of current_fsuid() for all fid lookups. Root is then unable to chown or perform other privileged operations. Fix by clearing the access mask before applying the user's choice.
Severity: 0.0 | NA
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