[PATCH] Fix security check for joint context= and fscontext= mount options

After some discussion on the actual meaning of the filesystem class
security check in try context mount it was determined that the checks for
the context= mount options were not correct if fscontext mount option had
already been used.

When labeling the superblock we should be checking relabel_from and
relabel_to.  But if the superblock has already been labeled (with
fscontext) then context= is actually labeling the inodes, and so we should
be checking relabel_from and associate.  This patch fixes which checks are
called depending on the mount options.
Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: James Morris <jmorris@namei.org>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

security/selinux/hooks.c

@@ -523,12 +523,16 @@ static int try_context_mount(struct super_block *sb, void *data)
 			goto out_free;
 		}
 
+		if (!fscontext) {
 			rc = may_context_mount_sb_relabel(sid, sbsec, tsec);
 			if (rc)
 				goto out_free;
-
-		if (!fscontext)
 			sbsec->sid = sid;
+		} else {
+			rc = may_context_mount_inode_relabel(sid, sbsec, tsec);
+			if (rc)
+				goto out_free;
+		}
 		sbsec->mntpoint_sid = sid;
 
 		sbsec->behavior = SECURITY_FS_USE_MNTPOINT;