[PATCH] lsm,nfs: fix NFS4 memory leak of lsm_context

[Stephen Smalley]

On Fri, Feb 21, 2025 at 10:59 AM Casey Schaufler <casey at schaufler-ca.com> wrote:
>
> The NFS4 security label code does not support multiple labels, and
> is intentionally unaware of which LSM is providing them. It is also
> the case that currently only one LSM that use security contexts is
> permitted to be active, as enforced by LSM_FLAG_EXCLUSIVE. Any LSM
> that receives a release_secctx that is not explicitly designated as
> for another LSM can safely carry out the release process. The NFS4
> code identifies the lsm_context as LSM_ID_UNDEF, so allowing the
> called LSM to perform the release is safe. Additional sophistication
> will be required when context using LSMs are allowed to be used
> together.

Shrug. This seems less safe to me but I will give it a try with
SELinux labeled NFS tests.

>
> Fixes: b530104f50e8 ("lsm: lsm_context in security_dentry_init_security")
> Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
> ---
>  security/apparmor/secid.c | 2 +-
>  security/selinux/hooks.c  | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/security/apparmor/secid.c b/security/apparmor/secid.c
> index 28caf66b9033..db484c214cda 100644
> --- a/security/apparmor/secid.c
> +++ b/security/apparmor/secid.c
> @@ -108,7 +108,7 @@ int apparmor_secctx_to_secid(const char *secdata, u32 seclen, u32 *secid)
>
>  void apparmor_release_secctx(struct lsm_context *cp)
>  {
> -       if (cp->id == LSM_ID_APPARMOR) {
> +       if (cp->id == LSM_ID_APPARMOR || cp->id == LSM_ID_UNDEF) {
>                 kfree(cp->context);
>                 cp->context = NULL;
>                 cp->id = LSM_ID_UNDEF;
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 7b867dfec88b..b89d3438b3df 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -6673,7 +6673,7 @@ static int selinux_secctx_to_secid(const char *secdata, u32 seclen, u32 *secid)
>
>  static void selinux_release_secctx(struct lsm_context *cp)
>  {
> -       if (cp->id == LSM_ID_SELINUX) {
> +       if (cp->id == LSM_ID_SELINUX || cp->id == LSM_ID_UNDEF) {
>                 kfree(cp->context);
>                 cp->context = NULL;
>                 cp->id = LSM_ID_UNDEF;
>