ovl: skip getxattr of security labels

When inode has no listxattr op of its own (e.g. squashfs) vfs_listxattr
calls the LSM inode_listsecurity hooks to list the xattrs that LSMs will
intercept in inode_getxattr hooks.

When selinux LSM is installed but not initialized, it will list the
security.selinux xattr in inode_listsecurity, but will not intercept it
in inode_getxattr.  This results in -ENODATA for a getxattr call for an
xattr returned by listxattr.

This situation was manifested as overlayfs failure to copy up lower
files from squashfs when selinux is built-in but not initialized,
because ovl_copy_xattr() iterates the lower inode xattrs by
vfs_listxattr() and vfs_getxattr().

ovl_copy_xattr() skips copy up of security labels that are indentified by
inode_copy_up_xattr LSM hooks, but it does that after vfs_getxattr().
Since we are not going to copy them, skip vfs_getxattr() of the security
labels.

Reported-by: Michael Labriola <michael.d.labriola@gmail.com>
Tested-by: Michael Labriola <michael.d.labriola@gmail.com>
Link: https://lore.kernel.org/linux-unionfs/2nv9d47zt7.fsf@aldarion.sourceruckus.org/
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index e5b616c..0fed532 100644 (file)
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -84,6 +84,14 @@ int ovl_copy_xattr(struct super_block *sb, struct dentry *old,
 
                if (ovl_is_private_xattr(sb, name))
                        continue;
+
+               error = security_inode_copy_up_xattr(name);
+               if (error < 0 && error != -EOPNOTSUPP)
+                       break;
+               if (error == 1) {
+                       error = 0;
+                       continue; /* Discard */
+               }
 retry:
                size = vfs_getxattr(old, name, value, value_size);
                if (size == -ERANGE)
@@ -107,13 +115,6 @@ retry:
                        goto retry;
                }
 
-               error = security_inode_copy_up_xattr(name);
-               if (error < 0 && error != -EOPNOTSUPP)
-                       break;
-               if (error == 1) {
-                       error = 0;
-                       continue; /* Discard */
-               }
                error = vfs_setxattr(new, name, value, size, 0);
                if (error) {
                        if (error != -EOPNOTSUPP || ovl_must_copy_xattr(name))