linux-kernel - Re: [PATCH v3 4/5] LSM: lsm_context in security_dentry_init

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Message-ID: <CAEjxPJ56H_Y-ObgNHrCggDK28NOARZ0CDmLDRvY5qgzu=YgE=A@mail.gmail.com>
Date: Thu, 20 Feb 2025 11:43:15 -0500
From: Stephen Smalley <stephen.smalley.work@...il.com>
To: Casey Schaufler <casey@...aufler-ca.com>
Cc: paul@...l-moore.com, linux-security-module@...r.kernel.org, 
	jmorris@...ei.org, serge@...lyn.com, keescook@...omium.org, 
	john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp, 
	linux-kernel@...r.kernel.org, selinux@...r.kernel.org, mic@...ikod.net, 
	ceph-devel@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: Re: [PATCH v3 4/5] LSM: lsm_context in security_dentry_init_security

On Wed, Oct 23, 2024 at 5:23 PM Casey Schaufler <casey@...aufler-ca.com> wrote:
>
> Replace the (secctx,seclen) pointer pair with a single lsm_context
> pointer to allow return of the LSM identifier along with the context
> and context length. This allows security_release_secctx() to know how
> to release the context. Callers have been modified to use or save the
> returned data from the new structure.
>
> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> Cc: ceph-devel@...r.kernel.org
> Cc: linux-nfs@...r.kernel.org
> ---
>  fs/ceph/super.h               |  3 +--
>  fs/ceph/xattr.c               | 16 ++++++----------
>  fs/fuse/dir.c                 | 35 ++++++++++++++++++-----------------
>  fs/nfs/nfs4proc.c             | 20 ++++++++++++--------
>  include/linux/lsm_hook_defs.h |  2 +-
>  include/linux/security.h      | 26 +++-----------------------
>  security/security.c           |  9 ++++-----
>  security/selinux/hooks.c      |  9 +++++----
>  8 files changed, 50 insertions(+), 70 deletions(-)
>

> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
> index 76776d716744..0b116ef3a752 100644
> --- a/fs/nfs/nfs4proc.c
> +++ b/fs/nfs/nfs4proc.c
> @@ -114,6 +114,7 @@ static inline struct nfs4_label *
>  nfs4_label_init_security(struct inode *dir, struct dentry *dentry,
>         struct iattr *sattr, struct nfs4_label *label)
>  {
> +       struct lsm_context shim;
>         int err;
>
>         if (label == NULL)
> @@ -128,21 +129,24 @@ nfs4_label_init_security(struct inode *dir, struct dentry *dentry,
>         label->label = NULL;
>
>         err = security_dentry_init_security(dentry, sattr->ia_mode,
> -                               &dentry->d_name, NULL,
> -                               (void **)&label->label, &label->len);
> -       if (err == 0)
> -               return label;
> +                               &dentry->d_name, NULL, &shim);
> +       if (err)
> +               return NULL;
>
> -       return NULL;
> +       label->label = shim.context;
> +       label->len = shim.len;
> +       return label;
>  }
>  static inline void
>  nfs4_label_release_security(struct nfs4_label *label)
>  {
> -       struct lsm_context scaff; /* scaffolding */
> +       struct lsm_context shim;
>
>         if (label) {
> -               lsmcontext_init(&scaff, label->label, label->len, 0);
> -               security_release_secctx(&scaff);
> +               shim.context = label->label;
> +               shim.len = label->len;
> +               shim.id = LSM_ID_UNDEF;

Is there a patch that follows this one to fix this? Otherwise, setting
this to UNDEF causes SELinux to NOT free the context, which produces a
memory leak for every NFS inode security context. Reported by kmemleak
when running the selinux-testsuite NFS tests.

> +               security_release_secctx(&shim);
>         }
>  }
>  static inline u32 *nfs4_bitmask(struct nfs_server *server, struct nfs4_label *label)