[v3] selinux: enable per-file labeling for functionfs

[PATCH v3] selinux: enable per-file labeling for functionfs

Posted by Neill Kapron 1 month ago

This patch adds support for genfscon per-file labeling of functionfs
files as well as support for userspace to apply labels after new
functionfs endpoints are created.

This allows for separate labels and therefore access control on a
per-endpoint basis. An example use case would be for the default
endpoint EP0 used as a restricted control endpoint, and additional
usb endpoints to be used by other more permissive domains.

It should be noted that if there are multiple functionfs mounts on a
system, genfs file labels will apply to all mounts, and therefore will not
likely be as useful as the userspace relabeling portion of this patch -
the addition to selinux_is_genfs_special_handling().

This patch introduces the functionfs_seclabel policycap to maintain
existing functionfs genfscon behavior unless explicitly enabled.

Signed-off-by: Neill Kapron <nkapron@google.com>

Changes since v1:
- Add functionfs_seclabel policycap
- Move new functionality to the end of existing lists

Changes since v2:
- Sending as separate patches
---
 security/selinux/hooks.c                   | 8 ++++++--
 security/selinux/include/policycap.h       | 1 +
 security/selinux/include/policycap_names.h | 1 +
 security/selinux/include/security.h        | 6 ++++++
 4 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index e474cd7398ef..333bb6cba25e 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -476,7 +476,9 @@ static int selinux_is_genfs_special_handling(struct super_block *sb)
 		!strcmp(sb->s_type->name, "rootfs") ||
 		(selinux_policycap_cgroupseclabel() &&
 		 (!strcmp(sb->s_type->name, "cgroup") ||
-		  !strcmp(sb->s_type->name, "cgroup2")));
+		  !strcmp(sb->s_type->name, "cgroup2"))) ||
+		(selinux_policycap_functionfs_seclabel() &&
+		 !strcmp(sb->s_type->name, "functionfs"));
 }
 
 static int selinux_is_sblabel_mnt(struct super_block *sb)
@@ -741,7 +743,9 @@ static int selinux_set_mnt_opts(struct super_block *sb,
 	    !strcmp(sb->s_type->name, "binder") ||
 	    !strcmp(sb->s_type->name, "bpf") ||
 	    !strcmp(sb->s_type->name, "pstore") ||
-	    !strcmp(sb->s_type->name, "securityfs"))
+	    !strcmp(sb->s_type->name, "securityfs") ||
+	    (selinux_policycap_functionfs_seclabel() &&
+	     strcmp(sb->s_type->name, "functionfs")))
 		sbsec->flags |= SE_SBGENFS;
 
 	if (!strcmp(sb->s_type->name, "sysfs") ||
diff --git a/security/selinux/include/policycap.h b/security/selinux/include/policycap.h
index 7405154e6c42..135a969f873c 100644
--- a/security/selinux/include/policycap.h
+++ b/security/selinux/include/policycap.h
@@ -17,6 +17,7 @@ enum {
 	POLICYDB_CAP_NETLINK_XPERM,
 	POLICYDB_CAP_NETIF_WILDCARD,
 	POLICYDB_CAP_GENFS_SECLABEL_WILDCARD,
+	POLICYDB_CAP_FUNCTIONFS_SECLABEL,
 	__POLICYDB_CAP_MAX
 };
 #define POLICYDB_CAP_MAX (__POLICYDB_CAP_MAX - 1)
diff --git a/security/selinux/include/policycap_names.h b/security/selinux/include/policycap_names.h
index d8962fcf2ff9..ff8882887651 100644
--- a/security/selinux/include/policycap_names.h
+++ b/security/selinux/include/policycap_names.h
@@ -20,6 +20,7 @@ const char *const selinux_policycap_names[__POLICYDB_CAP_MAX] = {
 	"netlink_xperm",
 	"netif_wildcard",
 	"genfs_seclabel_wildcard",
+	"functionfs_seclabel",
 };
 /* clang-format on */
 
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index 7f19972f7922..0f954a40d3fc 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -203,6 +203,12 @@ static inline bool selinux_policycap_netlink_xperm(void)
 		selinux_state.policycap[POLICYDB_CAP_NETLINK_XPERM]);
 }
 
+static inline bool selinux_policycap_functionfs_seclabel(void)
+{
+	return READ_ONCE(
+		selinux_state.policycap[POLICYDB_CAP_FUNCTIONFS_SECLABEL]);
+}
+
 struct selinux_policy_convert_data;
 
 struct selinux_load_state {
-- 
2.51.0.318.gd7df087d1a-goog

Re: [PATCH v3] selinux: enable per-file labeling for functionfs

Posted by Paul Moore 4 weeks ago

On Aug 28, 2025 Neill Kapron <nkapron@google.com> wrote:
> 
> This patch adds support for genfscon per-file labeling of functionfs
> files as well as support for userspace to apply labels after new
> functionfs endpoints are created.
> 
> This allows for separate labels and therefore access control on a
> per-endpoint basis. An example use case would be for the default
> endpoint EP0 used as a restricted control endpoint, and additional
> usb endpoints to be used by other more permissive domains.
> 
> It should be noted that if there are multiple functionfs mounts on a
> system, genfs file labels will apply to all mounts, and therefore will not
> likely be as useful as the userspace relabeling portion of this patch -
> the addition to selinux_is_genfs_special_handling().
> 
> This patch introduces the functionfs_seclabel policycap to maintain
> existing functionfs genfscon behavior unless explicitly enabled.
> 
> Signed-off-by: Neill Kapron <nkapron@google.com>
> 
> Changes since v1:
> - Add functionfs_seclabel policycap
> - Move new functionality to the end of existing lists
> 
> Changes since v2:
> - Sending as separate patches
> 
> Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>
> ---
>  security/selinux/hooks.c                   | 8 ++++++--
>  security/selinux/include/policycap.h       | 1 +
>  security/selinux/include/policycap_names.h | 1 +
>  security/selinux/include/security.h        | 6 ++++++
>  4 files changed, 14 insertions(+), 2 deletions(-)

Merged into selinux/dev, thanks!

--
paul-moore.com

Re: [PATCH v3] selinux: enable per-file labeling for functionfs

Posted by Neill Kapron 3 weeks, 6 days ago

On Thu, Sep 04, 2025 at 04:15:52PM -0400, Paul Moore wrote:
> 
> Merged into selinux/dev, thanks!
>

My appologies, I introduced a logic bug between v1 and v2, and have sent
a patch which fixes it [1].

Thanks,
Neill

[1] https://lore.kernel.org/selinux/20250905222656.3692837-1-nkapron@google.com/

Re: [PATCH v3] selinux: enable per-file labeling for functionfs

Posted by Stephen Smalley 1 month ago

On Thu, Aug 28, 2025 at 1:03 PM Neill Kapron <nkapron@google.com> wrote:
>
> This patch adds support for genfscon per-file labeling of functionfs
> files as well as support for userspace to apply labels after new
> functionfs endpoints are created.
>
> This allows for separate labels and therefore access control on a
> per-endpoint basis. An example use case would be for the default
> endpoint EP0 used as a restricted control endpoint, and additional
> usb endpoints to be used by other more permissive domains.
>
> It should be noted that if there are multiple functionfs mounts on a
> system, genfs file labels will apply to all mounts, and therefore will not
> likely be as useful as the userspace relabeling portion of this patch -
> the addition to selinux_is_genfs_special_handling().
>
> This patch introduces the functionfs_seclabel policycap to maintain
> existing functionfs genfscon behavior unless explicitly enabled.
>
> Signed-off-by: Neill Kapron <nkapron@google.com>

Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>

As before, don't rely on the policy capability bit remaining stable
until Paul merges this patch.
Also, not worth re-spinning IMHO but the changelog below normally goes
after the "---" before
the diffstat so that it doesn't get included in the commit message
since no one cares about
the in-submission changes once the patch is merged.

>
> Changes since v1:
> - Add functionfs_seclabel policycap
> - Move new functionality to the end of existing lists
>
> Changes since v2:
> - Sending as separate patches
> ---
>  security/selinux/hooks.c                   | 8 ++++++--
>  security/selinux/include/policycap.h       | 1 +
>  security/selinux/include/policycap_names.h | 1 +
>  security/selinux/include/security.h        | 6 ++++++
>  4 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index e474cd7398ef..333bb6cba25e 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -476,7 +476,9 @@ static int selinux_is_genfs_special_handling(struct super_block *sb)
>                 !strcmp(sb->s_type->name, "rootfs") ||
>                 (selinux_policycap_cgroupseclabel() &&
>                  (!strcmp(sb->s_type->name, "cgroup") ||
> -                 !strcmp(sb->s_type->name, "cgroup2")));
> +                 !strcmp(sb->s_type->name, "cgroup2"))) ||
> +               (selinux_policycap_functionfs_seclabel() &&
> +                !strcmp(sb->s_type->name, "functionfs"));
>  }
>
>  static int selinux_is_sblabel_mnt(struct super_block *sb)
> @@ -741,7 +743,9 @@ static int selinux_set_mnt_opts(struct super_block *sb,
>             !strcmp(sb->s_type->name, "binder") ||
>             !strcmp(sb->s_type->name, "bpf") ||
>             !strcmp(sb->s_type->name, "pstore") ||
> -           !strcmp(sb->s_type->name, "securityfs"))
> +           !strcmp(sb->s_type->name, "securityfs") ||
> +           (selinux_policycap_functionfs_seclabel() &&
> +            strcmp(sb->s_type->name, "functionfs")))
>                 sbsec->flags |= SE_SBGENFS;
>
>         if (!strcmp(sb->s_type->name, "sysfs") ||
> diff --git a/security/selinux/include/policycap.h b/security/selinux/include/policycap.h
> index 7405154e6c42..135a969f873c 100644
> --- a/security/selinux/include/policycap.h
> +++ b/security/selinux/include/policycap.h
> @@ -17,6 +17,7 @@ enum {
>         POLICYDB_CAP_NETLINK_XPERM,
>         POLICYDB_CAP_NETIF_WILDCARD,
>         POLICYDB_CAP_GENFS_SECLABEL_WILDCARD,
> +       POLICYDB_CAP_FUNCTIONFS_SECLABEL,
>         __POLICYDB_CAP_MAX
>  };
>  #define POLICYDB_CAP_MAX (__POLICYDB_CAP_MAX - 1)
> diff --git a/security/selinux/include/policycap_names.h b/security/selinux/include/policycap_names.h
> index d8962fcf2ff9..ff8882887651 100644
> --- a/security/selinux/include/policycap_names.h
> +++ b/security/selinux/include/policycap_names.h
> @@ -20,6 +20,7 @@ const char *const selinux_policycap_names[__POLICYDB_CAP_MAX] = {
>         "netlink_xperm",
>         "netif_wildcard",
>         "genfs_seclabel_wildcard",
> +       "functionfs_seclabel",
>  };
>  /* clang-format on */
>
> diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
> index 7f19972f7922..0f954a40d3fc 100644
> --- a/security/selinux/include/security.h
> +++ b/security/selinux/include/security.h
> @@ -203,6 +203,12 @@ static inline bool selinux_policycap_netlink_xperm(void)
>                 selinux_state.policycap[POLICYDB_CAP_NETLINK_XPERM]);
>  }
>
> +static inline bool selinux_policycap_functionfs_seclabel(void)
> +{
> +       return READ_ONCE(
> +               selinux_state.policycap[POLICYDB_CAP_FUNCTIONFS_SECLABEL]);
> +}
> +
>  struct selinux_policy_convert_data;
>
>  struct selinux_load_state {
> --
> 2.51.0.318.gd7df087d1a-goog
>

Re: [PATCH v3] selinux: enable per-file labeling for functionfs

Posted by Neill Kapron 1 month ago

On Fri, Aug 29, 2025 at 08:18:08AM -0400, Stephen Smalley wrote:
 
> As before, don't rely on the policy capability bit remaining stable
> until Paul merges this patch.
> Also, not worth re-spinning IMHO but the changelog below normally goes
> after the "---" before
> the diffstat so that it doesn't get included in the commit message
> since no one cares about
> the in-submission changes once the patch is merged.

Thanks, I appreciate your guidance on this!

Neill