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

…tions

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 <[email protected]>
Acked-by: Stephen Smalley <[email protected]>
Acked-by: James Morris <[email protected]>
Cc: Chris Wright <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

security/selinux/hooks.c

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