CVE-2026-52906
Beschrijving NL
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.
Origineel (Engels) tonen
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.