[PATCH] security/selinux: fix SECURITY_LSM_NATIVE_LABELS on reused superblock

From: bfields@fieldses.org (J. Bruce Fields)
To: Paul Moore <paul@paul-moore.com>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	Eric Paris <eparis@parisplace.org>
Cc: selinux@vger.kernel.org, Scott Mayhew <smayhew@redhat.com>
Subject: [PATCH] security/selinux: fix SECURITY_LSM_NATIVE_LABELS on reused superblock
Date: Tue, 5 Mar 2019 16:17:58 -0500	[thread overview]
Message-ID: <20190305211758.GA27437@fieldses.org> (raw)

From: "J. Bruce Fields" <bfields@redhat.com>

In the case when we're reusing a superblock, selinux_sb_clone_mnt_opts()
fails to set set_kern_flags, with the result that
nfs_clone_sb_security() incorrectly clears NFS_CAP_SECURITY_LABEL.

The result is that if you mount the same NFS filesystem twice, NFS
security labels are turned off, even if they would work fine if you
mounted the filesystem only once.

("fixes" may be not exactly the right tag, it may be more like
"fixed-other-cases-but-missed-this-one".)

Cc: Scott Mayhew <smayhew@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 0b4d3452b8b4 "security/selinux: allow security_sb_clone_mnt_opts..."
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
---
 security/selinux/hooks.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index f0e36c3492ba..5e9304567233 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -959,8 +959,11 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb,
 	BUG_ON(!(oldsbsec->flags & SE_SBINITIALIZED));
 
 	/* if fs is reusing a sb, make sure that the contexts match */
-	if (newsbsec->flags & SE_SBINITIALIZED)
+	if (newsbsec->flags & SE_SBINITIALIZED) {
+		if ((kern_flags & SECURITY_LSM_NATIVE_LABELS) && !set_context)
+			*set_kern_flags |= SECURITY_LSM_NATIVE_LABELS;
 		return selinux_cmp_sb_context(oldsb, newsb);
+	}
 
 	mutex_lock(&newsbsec->lock);
 
-- 
2.20.1

