selinux: preserve NATIVE_LABELS on already-initialized sb in set_mnt_opts

Overview

In the Linux kernel, the following vulnerability has been resolved:

selinux: preserve NATIVE_LABELS on already-initialized sb in set_mnt_opts

When an NFSv4 filesystem exported with security_label is mounted a second time, sget_fc() returns the existing superblock and nfs_get_root() calls security_sb_set_mnt_opts() again on it. Since the superblock is already SB_INITIALIZED, selinux_set_mnt_opts() takes an early exit without setting SECURITY_LSM_NATIVE_LABELS in *set_kern_flags. nfs_get_root() then sees kflags without SECURITY_LSM_NATIVE_LABELS set and clears NFS_CAP_SECURITY_LABEL on the shared nfs_server, silently disabling per-file labeling for both the new and the original mount.

Commit 3815a245b501 ("security/selinux: fix SECURITY_LSM_NATIVE_LABELS on reused superblock") fixed the same problem in selinux_sb_clone_mnt_opts(). The reused-superblock path for a plain second mount now goes through sb_set_mnt_opts rather than sb_clone_mnt_opts, so it needs the same treatment: on both SE_SBINITIALIZED early exits, set SECURITY_LSM_NATIVE_LABELS in *set_kern_flags when the superblock was already using SECURITY_FS_USE_NATVE.

Affected

• Linux >= eb9ae686507bc5a5ca78e6b3fbe629cd5cc67864 < a545def625860d4ccedc14fe45e884a62a041cef
• Linux >= eb9ae686507bc5a5ca78e6b3fbe629cd5cc67864 < a6da93c625b3557dd23ff6db45d2d1bafeae1565
• Linux >= eb9ae686507bc5a5ca78e6b3fbe629cd5cc67864 < 5509d498e1b9edafebd5a60ba3cb9ecfda23dc2b
• Linux >= eb9ae686507bc5a5ca78e6b3fbe629cd5cc67864 < c997832414f1d846de0a1fa38d7d4f62ba2ea917
• Linux >= eb9ae686507bc5a5ca78e6b3fbe629cd5cc67864 < 28b7260548af3d35773477993ad4e4de41578dd7
• Linux 3.11

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.