[PATCH v16 16/23] LSM: Use lsmcontext in security_inode_getsecctx

[Kees Cook]

On Mon, Apr 06, 2020 at 05:01:52PM -0700, Casey Schaufler wrote:
> Change the security_inode_getsecctx() interface to fill
> a lsmcontext structure instead of data and length pointers.
> This provides the information about which LSM created the
> context so that security_release_secctx() can use the
> correct hook.
> 
> Acked-by: Stephen Smalley <sds at tycho.nsa.gov>
> Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>

Reviewed-by: Kees Cook <keescook at chromium.org>

-Kees

> ---
>  fs/nfsd/nfs4xdr.c        | 23 +++++++++--------------
>  include/linux/security.h |  5 +++--
>  security/security.c      | 13 +++++++++++--
>  3 files changed, 23 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index df308b1b37fa..ac8eb77d0053 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -2379,11 +2379,11 @@ nfsd4_encode_layout_types(struct xdr_stream *xdr, u32 layout_types)
>  #ifdef CONFIG_NFSD_V4_SECURITY_LABEL
>  static inline __be32
>  nfsd4_encode_security_label(struct xdr_stream *xdr, struct svc_rqst *rqstp,
> -			    void *context, int len)
> +			    struct lsmcontext *context)
>  {
>  	__be32 *p;
>  
> -	p = xdr_reserve_space(xdr, len + 4 + 4 + 4);
> +	p = xdr_reserve_space(xdr, context->len + 4 + 4 + 4);
>  	if (!p)
>  		return nfserr_resource;
>  
> @@ -2393,13 +2393,13 @@ nfsd4_encode_security_label(struct xdr_stream *xdr, struct svc_rqst *rqstp,
>  	 */
>  	*p++ = cpu_to_be32(0); /* lfs */
>  	*p++ = cpu_to_be32(0); /* pi */
> -	p = xdr_encode_opaque(p, context, len);
> +	p = xdr_encode_opaque(p, context->context, context->len);
>  	return 0;
>  }
>  #else
>  static inline __be32
>  nfsd4_encode_security_label(struct xdr_stream *xdr, struct svc_rqst *rqstp,
> -			    void *context, int len)
> +			    struct lsmcontext *context)
>  { return 0; }
>  #endif
>  
> @@ -2496,9 +2496,7 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
>  	int err;
>  	struct nfs4_acl *acl = NULL;
>  #ifdef CONFIG_NFSD_V4_SECURITY_LABEL
> -	struct lsmcontext scaff; /* scaffolding */
> -	void *context = NULL;
> -	int contextlen;
> +	struct lsmcontext context = { };
>  #endif
>  	bool contextsupport = false;
>  	struct nfsd4_compoundres *resp = rqstp->rq_resp;
> @@ -2556,7 +2554,7 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
>  	     bmval0 & FATTR4_WORD0_SUPPORTED_ATTRS) {
>  		if (exp->ex_flags & NFSEXP_SECURITY_LABEL)
>  			err = security_inode_getsecctx(d_inode(dentry),
> -						&context, &contextlen);
> +						       &context);
>  		else
>  			err = -EOPNOTSUPP;
>  		contextsupport = (err == 0);
> @@ -2986,8 +2984,7 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
>  
>  #ifdef CONFIG_NFSD_V4_SECURITY_LABEL
>  	if (bmval2 & FATTR4_WORD2_SECURITY_LABEL) {
> -		status = nfsd4_encode_security_label(xdr, rqstp, context,
> -								contextlen);
> +		status = nfsd4_encode_security_label(xdr, rqstp, &context);
>  		if (status)
>  			goto out;
>  	}
> @@ -2999,10 +2996,8 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
>  
>  out:
>  #ifdef CONFIG_NFSD_V4_SECURITY_LABEL
> -	if (context) {
> -		lsmcontext_init(&scaff, context, contextlen, 0); /*scaffolding*/
> -		security_release_secctx(&scaff);
> -	}
> +	if (context.context)
> +		security_release_secctx(&context);
>  #endif /* CONFIG_NFSD_V4_SECURITY_LABEL */
>  	kfree(acl);
>  	if (tempfh) {
> diff --git a/include/linux/security.h b/include/linux/security.h
> index ec64ccd2e168..fac5547dd89e 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -556,7 +556,7 @@ void security_release_secctx(struct lsmcontext *cp);
>  void security_inode_invalidate_secctx(struct inode *inode);
>  int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
>  int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen);
> -int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
> +int security_inode_getsecctx(struct inode *inode, struct lsmcontext *cp);
>  int security_locked_down(enum lockdown_reason what);
>  #else /* CONFIG_SECURITY */
>  
> @@ -1382,7 +1382,8 @@ static inline int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32
>  {
>  	return -EOPNOTSUPP;
>  }
> -static inline int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen)
> +static inline int security_inode_getsecctx(struct inode *inode,
> +					   struct lsmcontext *cp)
>  {
>  	return -EOPNOTSUPP;
>  }
> diff --git a/security/security.c b/security/security.c
> index 356c5cd94c48..84f33bd4990a 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2211,9 +2211,18 @@ int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen)
>  }
>  EXPORT_SYMBOL(security_inode_setsecctx);
>  
> -int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen)
> +int security_inode_getsecctx(struct inode *inode, struct lsmcontext *cp)
>  {
> -	return call_int_hook(inode_getsecctx, -EOPNOTSUPP, inode, ctx, ctxlen);
> +	struct security_hook_list *hp;
> +
> +	memset(cp, 0, sizeof(*cp));
> +
> +	hlist_for_each_entry(hp, &security_hook_heads.inode_getsecctx, list) {
> +		cp->slot = hp->lsmid->slot;
> +		return hp->hook.inode_getsecctx(inode, (void **)&cp->context,
> +						&cp->len);
> +	}
> +	return -EOPNOTSUPP;
>  }
>  EXPORT_SYMBOL(security_inode_getsecctx);
>  
> -- 
> 2.24.1
> 

-- 
Kees Cook