Re: [PATCH RFC 4/5] selinux: Restrict cross-cgroup dma-heap charging

[Paul Moore <paul@paul-moore.com>]

On May 12, 2026 Albert Esteve <aesteve@redhat.com> wrote:
> 
> The security_dma_heap_alloc() hook allows security modules
> to control which processes may charge dma-buf allocations
> to another process's cgroup via the charge_pid_fd field of
> DMA_HEAP_IOCTL_ALLOC. Without a policy implementation, the
> hook is a no-op and the restriction is not enforced.
> 
> On SELinux-managed systems any domain with access to a
> dma-heap device node can therefore exhaust another cgroup's
> memory budget without restriction.
> 
> Implement selinux_dma_heap_alloc() using avc_has_perm() with
> a new dma_heap object class and a charge_to permission. Policy
> authors can then grant cross-cgroup charging selectively,
> for example:
> 
>   allow allocator_app_t client_app_t:dma_heap charge_to;
> 
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
>  security/selinux/hooks.c            | 7 +++++++
>  security/selinux/include/classmap.h | 1 +
>  2 files changed, 8 insertions(+)
> 
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 0f704380a8c81..ea1f410b9f619 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2189,6 +2189,12 @@ static int selinux_capable(const struct cred *cred, struct user_namespace *ns,
>  	return cred_has_capability(cred, cap, opts, ns == &init_user_ns);
>  }
>  
> +static int selinux_dma_heap_alloc(const struct cred *from, const struct cred *to)
> +{
> +	return avc_has_perm(cred_sid(from), cred_sid(to),
> +			    SECCLASS_DMA_HEAP, DMA_HEAP__CHARGE_TO, NULL);
> +}
> +
>  static int selinux_quotactl(int cmds, int type, int id, const struct super_block *sb)
>  {
>  	const struct cred *cred = current_cred();
> @@ -7541,6 +7547,7 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
>  	LSM_HOOK_INIT(capget, selinux_capget),
>  	LSM_HOOK_INIT(capset, selinux_capset),
>  	LSM_HOOK_INIT(capable, selinux_capable),
> +	LSM_HOOK_INIT(dma_heap_alloc, selinux_dma_heap_alloc),
>  	LSM_HOOK_INIT(quotactl, selinux_quotactl),
>  	LSM_HOOK_INIT(quota_on, selinux_quota_on),
>  	LSM_HOOK_INIT(syslog, selinux_syslog),
> diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
> index 90cb61b164256..d232f7808f6b8 100644
> --- a/security/selinux/include/classmap.h
> +++ b/security/selinux/include/classmap.h
> @@ -181,6 +181,7 @@ const struct security_class_mapping secclass_map[] = {
>  	{ "user_namespace", { "create", NULL } },
>  	{ "memfd_file",
>  	  { COMMON_FILE_PERMS, "execute_no_trans", "entrypoint", NULL } },
> +	{ "dma_heap", { "charge_to", NULL } },
>  	/* last one */ { NULL, {} }
>  };

While we have seen some one-off patches to add specific resource/cgroups
controls in the past, much like this one, we've yet to see a patchset
that provides a more comprehensive set of resource/cgroup access controls
for SELinux.

I'm not opposed to a patch like this, but I would like to see it as part
of a larger effort to introduce access controls across all of the
existing cgroup control points where it makes sense.  In other words,
let's see a design for cgroup access controls so that we can ensure we
have something that is meaningful and makes sense from a policy
developer's perspective.

--
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