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Message-ID: <CAEjxPJ5KTJ1DDaAJ89sSdxUetbP_5nHB5OZ0qL18m4b_5N10-w@mail.gmail.com>
Date: Thu, 20 Feb 2025 13:16:56 -0500
From: Stephen Smalley <stephen.smalley.work@...il.com>
To: Paul Moore <paul@...l-moore.com>
Cc: Casey Schaufler <casey@...aufler-ca.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 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>
---
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;
};
--
2.48.1
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