[v2,12/25] selinux: add hooks for fscaps operations

  Add hooks for set/get/remove fscaps operations which perform the same
checks as the xattr hooks would have done for XATTR_NAME_CAPS.

Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
---
 security/selinux/hooks.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)
  

On Wed, Feb 21, 2024 at 4:25 PM Seth Forshee (DigitalOcean)
<sforshee@kernel.org> wrote:
>
> Add hooks for set/get/remove fscaps operations which perform the same
> checks as the xattr hooks would have done for XATTR_NAME_CAPS.
>
> Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
> ---
>  security/selinux/hooks.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index a6bf90ace84c..da129a387b34 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3367,6 +3367,29 @@ static int selinux_inode_removexattr(struct mnt_idmap *idmap,
>         return -EACCES;
>  }
>
> +static int selinux_inode_set_fscaps(struct mnt_idmap *idmap,
> +                                   struct dentry *dentry,
> +                                   const struct vfs_caps *caps, int flags)
> +{
> +       return dentry_has_perm(current_cred(), dentry, FILE__SETATTR);
> +}

The selinux_inode_setxattr() code also has a cap_inode_setxattr()
check which is missing here.  Unless you are handling this somewhere
else, I would expect the function above to look similar to
selinux_inode_remove_fscaps(), but obviously tweaked for setting the
fscaps and not removing them.

> +static int selinux_inode_get_fscaps(struct mnt_idmap *idmap,
> +                                   struct dentry *dentry)
> +{
> +       return dentry_has_perm(current_cred(), dentry, FILE__GETATTR);
> +}
> +
> +static int selinux_inode_remove_fscaps(struct mnt_idmap *idmap,
> +                                      struct dentry *dentry)
> +{
> +       int rc = cap_inode_removexattr(idmap, dentry, XATTR_NAME_CAPS);
> +       if (rc)
> +               return rc;
> +
> +       return dentry_has_perm(current_cred(), dentry, FILE__SETATTR);
> +}
> +
>  static int selinux_path_notify(const struct path *path, u64 mask,
>                                                 unsigned int obj_type)
>  {
> @@ -7165,6 +7188,9 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
>         LSM_HOOK_INIT(inode_set_acl, selinux_inode_set_acl),
>         LSM_HOOK_INIT(inode_get_acl, selinux_inode_get_acl),
>         LSM_HOOK_INIT(inode_remove_acl, selinux_inode_remove_acl),
> +       LSM_HOOK_INIT(inode_set_fscaps, selinux_inode_set_fscaps),
> +       LSM_HOOK_INIT(inode_get_fscaps, selinux_inode_get_fscaps),
> +       LSM_HOOK_INIT(inode_remove_fscaps, selinux_inode_remove_fscaps),
>         LSM_HOOK_INIT(inode_getsecurity, selinux_inode_getsecurity),
>         LSM_HOOK_INIT(inode_setsecurity, selinux_inode_setsecurity),
>         LSM_HOOK_INIT(inode_listsecurity, selinux_inode_listsecurity),
>
> --
> 2.43.0
  

On Wed, Feb 21, 2024 at 06:38:33PM -0500, Paul Moore wrote:
> On Wed, Feb 21, 2024 at 4:25 PM Seth Forshee (DigitalOcean)
> <sforshee@kernel.org> wrote:
> >
> > Add hooks for set/get/remove fscaps operations which perform the same
> > checks as the xattr hooks would have done for XATTR_NAME_CAPS.
> >
> > Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
> > ---
> >  security/selinux/hooks.c | 26 ++++++++++++++++++++++++++
> >  1 file changed, 26 insertions(+)
> >
> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > index a6bf90ace84c..da129a387b34 100644
> > --- a/security/selinux/hooks.c
> > +++ b/security/selinux/hooks.c
> > @@ -3367,6 +3367,29 @@ static int selinux_inode_removexattr(struct mnt_idmap *idmap,
> >         return -EACCES;
> >  }
> >
> > +static int selinux_inode_set_fscaps(struct mnt_idmap *idmap,
> > +                                   struct dentry *dentry,
> > +                                   const struct vfs_caps *caps, int flags)
> > +{
> > +       return dentry_has_perm(current_cred(), dentry, FILE__SETATTR);
> > +}
> 
> The selinux_inode_setxattr() code also has a cap_inode_setxattr()
> check which is missing here.  Unless you are handling this somewhere
> else, I would expect the function above to look similar to
> selinux_inode_remove_fscaps(), but obviously tweaked for setting the
> fscaps and not removing them.

Right, but cap_inode_setxattr() doesn't do anything for fscaps, so I
omitted the call. Unless you think the call should be included in case
cap_inode_setxattr() changes in the future, which is a reasonable
position.

Thanks,
Seth
  

On Wed, Feb 21, 2024 at 7:10 PM Seth Forshee (DigitalOcean)
<sforshee@kernel.org> wrote:
> On Wed, Feb 21, 2024 at 06:38:33PM -0500, Paul Moore wrote:
> > On Wed, Feb 21, 2024 at 4:25 PM Seth Forshee (DigitalOcean)
> > <sforshee@kernel.org> wrote:
> > >
> > > Add hooks for set/get/remove fscaps operations which perform the same
> > > checks as the xattr hooks would have done for XATTR_NAME_CAPS.
> > >
> > > Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
> > > ---
> > >  security/selinux/hooks.c | 26 ++++++++++++++++++++++++++
> > >  1 file changed, 26 insertions(+)
> > >
> > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > > index a6bf90ace84c..da129a387b34 100644
> > > --- a/security/selinux/hooks.c
> > > +++ b/security/selinux/hooks.c
> > > @@ -3367,6 +3367,29 @@ static int selinux_inode_removexattr(struct mnt_idmap *idmap,
> > >         return -EACCES;
> > >  }
> > >
> > > +static int selinux_inode_set_fscaps(struct mnt_idmap *idmap,
> > > +                                   struct dentry *dentry,
> > > +                                   const struct vfs_caps *caps, int flags)
> > > +{
> > > +       return dentry_has_perm(current_cred(), dentry, FILE__SETATTR);
> > > +}
> >
> > The selinux_inode_setxattr() code also has a cap_inode_setxattr()
> > check which is missing here.  Unless you are handling this somewhere
> > else, I would expect the function above to look similar to
> > selinux_inode_remove_fscaps(), but obviously tweaked for setting the
> > fscaps and not removing them.
>
> Right, but cap_inode_setxattr() doesn't do anything for fscaps, so I
> omitted the call. Unless you think the call should be included in case
> cap_inode_setxattr() changes in the future, which is a reasonable
> position.

Fair enough, but I'd be a lot happier if you included the call in case
something changes in the future.  I worry that omitting the call would
make it easier for us to forget about this if/when things change and
suddenly we have a security issue.  If you are morally opposed to
that, at the very least put a comment in selinux_inode_set_fscaps()
about this so we know who to yell at in the future ;)
  

On Wed, Feb 21, 2024 at 07:19:07PM -0500, Paul Moore wrote:
> On Wed, Feb 21, 2024 at 7:10 PM Seth Forshee (DigitalOcean)
> <sforshee@kernel.org> wrote:
> > On Wed, Feb 21, 2024 at 06:38:33PM -0500, Paul Moore wrote:
> > > On Wed, Feb 21, 2024 at 4:25 PM Seth Forshee (DigitalOcean)
> > > <sforshee@kernel.org> wrote:
> > > >
> > > > Add hooks for set/get/remove fscaps operations which perform the same
> > > > checks as the xattr hooks would have done for XATTR_NAME_CAPS.
> > > >
> > > > Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
> > > > ---
> > > >  security/selinux/hooks.c | 26 ++++++++++++++++++++++++++
> > > >  1 file changed, 26 insertions(+)
> > > >
> > > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > > > index a6bf90ace84c..da129a387b34 100644
> > > > --- a/security/selinux/hooks.c
> > > > +++ b/security/selinux/hooks.c
> > > > @@ -3367,6 +3367,29 @@ static int selinux_inode_removexattr(struct mnt_idmap *idmap,
> > > >         return -EACCES;
> > > >  }
> > > >
> > > > +static int selinux_inode_set_fscaps(struct mnt_idmap *idmap,
> > > > +                                   struct dentry *dentry,
> > > > +                                   const struct vfs_caps *caps, int flags)
> > > > +{
> > > > +       return dentry_has_perm(current_cred(), dentry, FILE__SETATTR);
> > > > +}
> > >
> > > The selinux_inode_setxattr() code also has a cap_inode_setxattr()
> > > check which is missing here.  Unless you are handling this somewhere
> > > else, I would expect the function above to look similar to
> > > selinux_inode_remove_fscaps(), but obviously tweaked for setting the
> > > fscaps and not removing them.
> >
> > Right, but cap_inode_setxattr() doesn't do anything for fscaps, so I
> > omitted the call. Unless you think the call should be included in case
> > cap_inode_setxattr() changes in the future, which is a reasonable
> > position.
> 
> Fair enough, but I'd be a lot happier if you included the call in case
> something changes in the future.  I worry that omitting the call would
> make it easier for us to forget about this if/when things change and
> suddenly we have a security issue.  If you are morally opposed to
> that, at the very least put a comment in selinux_inode_set_fscaps()
> about this so we know who to yell at in the future ;)

Makes sense, no objection from me. I'll add it in for v3.