[PATCH v2 1/2] selinux: enable per-file labeling for functionfs

[PATCH v2 1/2] selinux: enable per-file labeling for functionfs

[Neill Kapron]

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
---
 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

[PATCH v2 2/2] libsepol: Support functionfs_seclabel policycap

[Neill Kapron]

This adds the necessary userspace pieces to support the
functionfs_seclabel policycap which enables per-file labels in
functionfs and the ability for userspace to apply the labels.

With the policycap disabled, legacy behaviors are maintained and
per-file labeling is disallowed.

Signed-off-by: Neill Kapron <nkapron@google.com>
---
 libsepol/include/sepol/policydb/polcaps.h | 1 +
 libsepol/src/polcaps.c                    | 1 +
 2 files changed, 2 insertions(+)

diff --git a/libsepol/include/sepol/policydb/polcaps.h b/libsepol/include/sepol/policydb/polcaps.h
index 0835ea21..bbaebf1a 100644
--- a/libsepol/include/sepol/policydb/polcaps.h
+++ b/libsepol/include/sepol/policydb/polcaps.h
@@ -19,6 +19,7 @@ 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/libsepol/src/polcaps.c b/libsepol/src/polcaps.c
index 7ac0ae7c..83eb6143 100644
--- a/libsepol/src/polcaps.c
+++ b/libsepol/src/polcaps.c
@@ -18,6 +18,7 @@ static const char * const polcap_names[POLICYDB_CAP_MAX + 1] = {
 	[POLICYDB_CAP_NETLINK_XPERM]			= "netlink_xperm",
 	[POLICYDB_CAP_NETIF_WILDCARD]			= "netif_wildcard",
 	[POLICYDB_CAP_GENFS_SECLABEL_WILDCARD]		= "genfs_seclabel_wildcard",
+	[POLICYDB_CAP_FUNCTIONFS_SECLABEL]		= "functionfs_seclabel",
 };
 
 int sepol_polcap_getnum(const char *name)
-- 
2.51.0.318.gd7df087d1a-goog

Re: [PATCH v2 2/2] libsepol: Support functionfs_seclabel policycap

[Stephen Smalley]

On Wed, Aug 27, 2025 at 6:22 PM Neill Kapron <nkapron@google.com> wrote:
>
> This adds the necessary userspace pieces to support the
> functionfs_seclabel policycap which enables per-file labels in
> functionfs and the ability for userspace to apply the labels.
>
> With the policycap disabled, legacy behaviors are maintained and
> per-file labeling is disallowed.
>
> Signed-off-by: Neill Kapron <nkapron@google.com>

Just a note for other SELinux userspace maintainers: we need to
de-conflict the currently pending 3 kernel patches each trying to
claim the next available policy capability bit so don't merge any of
the libsepol patches until that gets resolved please.


> ---
>  libsepol/include/sepol/policydb/polcaps.h | 1 +
>  libsepol/src/polcaps.c                    | 1 +
>  2 files changed, 2 insertions(+)
>
> diff --git a/libsepol/include/sepol/policydb/polcaps.h b/libsepol/include/sepol/policydb/polcaps.h
> index 0835ea21..bbaebf1a 100644
> --- a/libsepol/include/sepol/policydb/polcaps.h
> +++ b/libsepol/include/sepol/policydb/polcaps.h
> @@ -19,6 +19,7 @@ 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/libsepol/src/polcaps.c b/libsepol/src/polcaps.c
> index 7ac0ae7c..83eb6143 100644
> --- a/libsepol/src/polcaps.c
> +++ b/libsepol/src/polcaps.c
> @@ -18,6 +18,7 @@ static const char * const polcap_names[POLICYDB_CAP_MAX + 1] = {
>         [POLICYDB_CAP_NETLINK_XPERM]                    = "netlink_xperm",
>         [POLICYDB_CAP_NETIF_WILDCARD]                   = "netif_wildcard",
>         [POLICYDB_CAP_GENFS_SECLABEL_WILDCARD]          = "genfs_seclabel_wildcard",
> +       [POLICYDB_CAP_FUNCTIONFS_SECLABEL]              = "functionfs_seclabel",
>  };
>
>  int sepol_polcap_getnum(const char *name)
> --
> 2.51.0.318.gd7df087d1a-goog
>

Re: [PATCH v2 1/2] selinux: enable per-file labeling for functionfs

[Stephen Smalley]

On Wed, Aug 27, 2025 at 6:22 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>
>
> Changes since v1:
> - Add functionfs_seclabel policycap
> - Move new functionality to the end of existing lists

This isn't actually a multi-patch series for the kernel, so don't use
the patch 1/2, patch 2/2 notation since that confuses b4 (it tries to
pull in the 2nd patch for libsepol and unsurprisingly that won't apply
to the kernel). Not sure that warrants re-posting (defer to Paul). The
patch itself looks fine to me but we now have 3 pending patches each
of which is trying to claim the next available policy capability bit,
so we'll ultimately need to de-conflict for upstream merge. Otherwise,
you can add my:

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(-)
>
> 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 v2 1/2] selinux: enable per-file labeling for functionfs

[Neill Kapron]

On Thu, Aug 28, 2025 at 09:08:48AM -0400, Stephen Smalley wrote:
 
> This isn't actually a multi-patch series for the kernel, so don't use
> the patch 1/2, patch 2/2 notation since that confuses b4 (it tries to
> pull in the 2nd patch for libsepol and unsurprisingly that won't apply
> to the kernel). Not sure that warrants re-posting (defer to Paul).

Whoops, I will send separate patches as v3.

Thanks,
Neill