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Message-ID: <CAEjxPJ44NNZU7u7vLN_Oj4jeptZ=Mb9RkKvJtL=xGciXOWDmKA@mail.gmail.com>
Date: Thu, 20 Feb 2025 14:37:19 -0500
From: Stephen Smalley <stephen.smalley.work@...il.com>
To: Casey Schaufler <casey@...aufler-ca.com>
Cc: Paul Moore <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 Thu, Feb 20, 2025 at 2:33 PM Casey Schaufler <casey@...aufler-ca.com> wrote:
>
> On 2/20/2025 10:16 AM, Stephen Smalley wrote:
> > On Thu, Feb 20, 2025 at 1:02 PM Stephen Smalley
> > <stephen.smalley.work@...il.com> wrote:
> >> On Thu, Feb 20, 2025 at 12:54 PM Paul Moore <paul@...l-moore.com> wrote:
> >>> On Thu, Feb 20, 2025 at 12:40 PM Paul Moore <paul@...l-moore.com> wrote:
> >>>> On Thu, Feb 20, 2025 at 11:43 AM Stephen Smalley
> >>>> <stephen.smalley.work@...il.com> wrote:
> >>>>> 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.
> >>>> 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.
> > Something like this (not tested yet). If this looks sane, will submit
> > separately.
> >
> > commit b530104f50e8 ("lsm: lsm_context in security_dentry_init_security")
> > did not preserve the lsm id for subsequent release calls, which results
> > in a memory leak. Fix it by saving the lsm id in the nfs4_label and
> > providing it on the subsequent release call.
> >
> > Fixes: b530104f50e8 ("lsm: lsm_context in security_dentry_init_security")
> > Signed-off-by: Stephen Smalley <stephen.smalley.work@...il.com>
>
> I'm not a fan of adding secids into other subsystems, especially in cases
> where they've tried to avoid them in the past.
>
> The better solution, which I'm tracking down the patch for now, is for
> the individual LSMs to always do their release, and for security_release_secctx()
> to check the lsm_id and call the appropriate LSM specific hook. Until there
> are multiple LSMs with contexts, LSM_ID_UNDEF is as good as a match.
>
> Please don't use this patch.
It doesn't add a secid; it just saves the LSM id obtained from
lsm_context populated by the security_dentry_init_security() hook call
and passes it back in the lsm_context to the security_release_secctx()
call.
>
> > ---
> > fs/nfs/nfs4proc.c | 7 ++++---
> > include/linux/nfs4.h | 1 +
> > 2 files changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
> > index df9669d4ded7..c0caaec7bd20 100644
> > --- a/fs/nfs/nfs4proc.c
> > +++ b/fs/nfs/nfs4proc.c
> > @@ -133,6 +133,7 @@ nfs4_label_init_security(struct inode *dir, struct
> > dentry *dentry,
> > if (err)
> > return NULL;
> >
> > + label->lsmid = shim.id;
> > label->label = shim.context;
> > label->len = shim.len;
> > return label;
> > @@ -145,7 +146,7 @@ nfs4_label_release_security(struct nfs4_label *label)
> > if (label) {
> > shim.context = label->label;
> > shim.len = label->len;
> > - shim.id = LSM_ID_UNDEF;
> > + shim.id = label->lsmid;
> > security_release_secctx(&shim);
> > }
> > }
> > @@ -6269,7 +6270,7 @@ static int _nfs4_get_security_label(struct inode
> > *inode, void *buf,
> > size_t buflen)
> > {
> > struct nfs_server *server = NFS_SERVER(inode);
> > - struct nfs4_label label = {0, 0, buflen, buf};
> > + struct nfs4_label label = {0, 0, 0, buflen, buf};
> >
> > u32 bitmask[3] = { 0, 0, FATTR4_WORD2_SECURITY_LABEL };
> > struct nfs_fattr fattr = {
> > @@ -6374,7 +6375,7 @@ static int nfs4_do_set_security_label(struct inode *inode,
> > static int
> > nfs4_set_security_label(struct inode *inode, const void *buf, size_t buflen)
> > {
> > - struct nfs4_label ilabel = {0, 0, buflen, (char *)buf };
> > + struct nfs4_label ilabel = {0, 0, 0, buflen, (char *)buf };
> > struct nfs_fattr *fattr;
> > int status;
> >
> > diff --git a/include/linux/nfs4.h b/include/linux/nfs4.h
> > index 71fbebfa43c7..9ac83ca88326 100644
> > --- a/include/linux/nfs4.h
> > +++ b/include/linux/nfs4.h
> > @@ -47,6 +47,7 @@ struct nfs4_acl {
> > struct nfs4_label {
> > uint32_t lfs;
> > uint32_t pi;
> > + u32 lsmid;
> > u32 len;
> > char *label;
> > };
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