Re: [PATCH v3 4/5] LSM: lsm_context in security_dentry_init_security

[Casey Schaufler <casey@schaufler-ca.com>]

On 2/20/2025 9:40 AM, Paul Moore wrote:
> On Thu, Feb 20, 2025 at 11:43 AM Stephen Smalley
> <stephen.smalley.work@gmail.com> wrote:
>> On Wed, Oct 23, 2024 at 5:23 PM Casey Schaufler <casey@schaufler-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@schaufler-ca.com>
>>> Cc: ceph-devel@vger.kernel.org
>>> Cc: linux-nfs@vger.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.
> I don't recall seeing anything related to this, but patches are
> definitely welcome.

I'm looking into this but as you well know the NFS tests aren't
always especially cooperative.