From 1ca924044bf0de879a1648be93a56939652267d3 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Christian=20G=C3=B6ttsche?= Date: Wed, 23 Sep 2026 12:13:23 +0200 Subject: [PATCH 1/2] selinux: fix data race on AVC latest_notif MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit avc_policy_seqno() reads latest_notif without holding notif_lock, while avc_latest_notif_update() can update it under that lock. KCSAN reports these concurrent accesses during policy boolean updates and permission checks. Use READ_ONCE() for the lockless read and WRITE_ONCE() for the update. The spinlock continues to serialize the comparison and update against other writers. Reads made while holding notif_lock cannot race with a writer and can remain plain accesses. This marks both sides of the intentional concurrent access and constrains compiler transformations, without suppressing checking with data_race(). Cc: stable@vger.kernel.org Fixes: 788e7dd4c22e ("SELinux: Improve read/write performance") Reported-by: syzbot+a7f7cb0737bd91aa698c@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=a7f7cb0737bd91aa698c Signed-off-by: Christian Göttsche Acked-by: Stephen Smalley Signed-off-by: Paul Moore --- security/selinux/avc.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/security/selinux/avc.c b/security/selinux/avc.c index 560a82c6d682..b91f914d292e 100644 --- a/security/selinux/avc.c +++ b/security/selinux/avc.c @@ -578,7 +578,7 @@ static int avc_latest_notif_update(u32 seqno, int is_insert) } } else { if (seqno > selinux_avc.avc_cache.latest_notif) - selinux_avc.avc_cache.latest_notif = seqno; + WRITE_ONCE(selinux_avc.avc_cache.latest_notif, seqno); } spin_unlock_irqrestore(¬if_lock, flag); @@ -1206,5 +1206,6 @@ int avc_has_perm(u32 ssid, u32 tsid, u16 tclass, u32 avc_policy_seqno(void) { - return selinux_avc.avc_cache.latest_notif; + /* Writers hold notif_lock; readers only sample the sequence number. */ + return READ_ONCE(selinux_avc.avc_cache.latest_notif); } From 28b7260548af3d35773477993ad4e4de41578dd7 Mon Sep 17 00:00:00 2001 From: Stephen Smalley Date: Mon, 28 Sep 2026 10:19:17 -0400 Subject: [PATCH 2/2] 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. Cc: stable@vger.kernel.org Closes: https://github.com/SELinuxProject/selinux-kernel/issues/69 Closes: https://github.com/SELinuxProject/selinux-kernel/issues/70 Closes: https://github.com/SELinuxProject/selinux-testsuite/issues/91 Closes: https://github.com/SELinuxProject/selinux-testsuite/issues/92 Fixes: eb9ae686507b ("SELinux: Add new labeling type native labels") Signed-off-by: Stephen Smalley Signed-off-by: Paul Moore --- security/selinux/hooks.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 3f4a6ddee322..30776b0107f2 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -690,8 +690,12 @@ static int selinux_set_mnt_opts(struct super_block *sb, * will be used for both mounts) */ if ((sbsec->flags & SE_SBINITIALIZED) && (sb->s_type->fs_flags & FS_BINARY_MOUNTDATA) - && !opts) + && !opts) { + if ((kern_flags & SECURITY_LSM_NATIVE_LABELS) && + sbsec->behavior == SECURITY_FS_USE_NATIVE) + *set_kern_flags |= SECURITY_LSM_NATIVE_LABELS; goto out; + } root_isec = backing_inode_security_novalidate(root); @@ -735,6 +739,9 @@ static int selinux_set_mnt_opts(struct super_block *sb, /* previously mounted with options, but not on this attempt? */ if ((sbsec->flags & SE_MNTMASK) && !opts) goto out_double_mount; + if ((kern_flags & SECURITY_LSM_NATIVE_LABELS) && + sbsec->behavior == SECURITY_FS_USE_NATIVE) + *set_kern_flags |= SECURITY_LSM_NATIVE_LABELS; rc = 0; goto out; }