[PATCH] selinux: fix inconsistency between inode_getxattr and inode_listsecurity

[Ondrej Mosnacek]

On Sat, Dec 19, 2020 at 11:07 AM Amir Goldstein <amir73il at gmail.com> wrote:
> 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().
>
> Match the logic of inode_listsecurity to that of inode_getxattr and
> do not list the security.selinux xattr if selinux is not initialized.
>
> Reported-by: Michael Labriola <michael.d.labriola at gmail.com>
> Tested-by: Michael Labriola <michael.d.labriola at gmail.com>
> Link: https://lore.kernel.org/linux-unionfs/2nv9d47zt7.fsf@aldarion.sourceruckus.org/
> Fixes: c8e222616c7e ("selinux: allow reading labels before policy is loaded")
> Cc: stable at vger.kernel.org#v5.9+
> Signed-off-by: Amir Goldstein <amir73il at gmail.com>
> ---
>  security/selinux/hooks.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 6b1826fc3658..e132e082a5af 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3406,6 +3406,10 @@ static int selinux_inode_setsecurity(struct inode *inode, const char *name,
>  static int selinux_inode_listsecurity(struct inode *inode, char *buffer, size_t buffer_size)
>  {
>         const int len = sizeof(XATTR_NAME_SELINUX);
> +
> +       if (!selinux_initialized(&selinux_state))
> +               return 0;
> +
>         if (buffer && len <= buffer_size)
>                 memcpy(buffer, XATTR_NAME_SELINUX, len);
>         return len;
> --
> 2.25.1

Looked at the logic in vfs_listxattr() and this looks reasonable.

Reviewed-by: Ondrej Mosnacek <omosnace at redhat.com>

Thank you for the patch!

-- 
Ondrej Mosnacek
Software Engineer, Platform Security - SELinux kernel
Red Hat, Inc.