On 2/20/2025 10:02 AM, Stephen Smalley wrote:
> On Thu, Feb 20, 2025 at 12:54 PM Paul Moore <paul@xxxxxxxxxxxxxx> wrote:
>> On Thu, Feb 20, 2025 at 12:40 PM Paul Moore <paul@xxxxxxxxxxxxxx> wrote:
>>> On Thu, Feb 20, 2025 at 11:43 AM Stephen Smalley
>>> <stephen.smalley.work@xxxxxxxxx> wrote:
>>>> On Wed, Oct 23, 2024 at 5:23 PM Casey Schaufler <casey@xxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxx>
>>>>> Cc: ceph-devel@xxxxxxxxxxxxxxx
>>>>> Cc: linux-nfs@xxxxxxxxxxxxxxx
>>>>> ---
>>>>> 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.
>> Looking at this quickly, this is an interesting problem as I don't
>> believe we have enough context in nfs4_label_release_security() to
>> correctly set the shim.id value. If there is a positive, it is that
>> lsm_context is really still just a string wrapped up with some
>> metadata, e.g. length/ID, so we kfree()'ing shim.context is going to
>> be okay-ish, at least for the foreseeable future.
>>
>> I can think of two ways to fix this, but I'd love to hear other ideas too.
>>
>> 1. Handle the LSM_ID_UNDEF case directly in security_release_secctx()
>> and skip any individual LSM processing.
>>
>> 2. Define a new LSM_ID_ANY value and update all of the LSMs to also
>> process the ANY case as well as their own.
>>
>> I'm not finding either option very exciting, but option #2 looks
>> particularly ugly, so I think I'd prefer to see someone draft a patch
>> for option #1 assuming nothing better is presented.
> We could perhaps add a u32 lsmid to struct nfs4_label, save it from
> the shim.id obtained in nfs4_label_init_security(), and use it in
> nfs4_label_release_security(). Not sure why that wasn't done in the
> first place.
This is all an artifact of breaking up and rearranging the full
stacking patches. My bad. I have to find where the logic for releasing
this got lost.
