[PATCH] selinux: fix inconsistency between inode_getxattr and inode_listsecurity

[PATCH] selinux: fix inconsistency between inode_getxattr and inode_listsecurity

[Amir Goldstein]

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@gmail.com>
Tested-by: Michael Labriola <michael.d.labriola@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@vger.kernel.org#v5.9+
Signed-off-by: Amir Goldstein <amir73il@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

Re: [PATCH] selinux: fix inconsistency between inode_getxattr and inode_listsecurity

[Ondrej Mosnacek]

On Sat, Dec 19, 2020 at 11:07 AM Amir Goldstein <amir73il@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@gmail.com>
> Tested-by: Michael Labriola <michael.d.labriola@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@vger.kernel.org#v5.9+
> Signed-off-by: Amir Goldstein <amir73il@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@redhat.com>

Thank you for the patch!

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

Re: [PATCH] selinux: fix inconsistency between inode_getxattr and inode_listsecurity

[Paul Moore]

On Mon, Jan 4, 2021 at 4:39 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> On Sat, Dec 19, 2020 at 11:07 AM Amir Goldstein <amir73il@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@gmail.com>
> > Tested-by: Michael Labriola <michael.d.labriola@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@vger.kernel.org#v5.9+
> > Signed-off-by: Amir Goldstein <amir73il@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.

Agreed, this looks good to me too; I'll merge it into selinux/next.
Thanks everyone!

-- 
paul moore
www.paul-moore.com