[PATCH 5.0 155/238] security/selinux: fix SECURITY_LSM_NATIVE_LABELS on reused superblock

[Greg Kroah-Hartman]

5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: J. Bruce Fields <bfields@xxxxxxxxxx>

commit 3815a245b50124f0865415dcb606a034e97494d4 upstream.

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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 0b4d3452b8b4 "security/selinux: allow security_sb_clone_mnt_opts..."
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Acked-by: Stephen Smalley <sds@xxxxxxxxxxxxx>
Signed-off-by: Paul Moore <paul@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 security/selinux/hooks.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -959,8 +959,11 @@ static int selinux_sb_clone_mnt_opts(con
 	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);