From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 131A2E95A9E for ; Mon, 9 Oct 2023 15:37:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377117AbjJIPhz (ORCPT ); Mon, 9 Oct 2023 11:37:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44762 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1377697AbjJIPhm (ORCPT ); Mon, 9 Oct 2023 11:37:42 -0400 Received: from smtp-42af.mail.infomaniak.ch (smtp-42af.mail.infomaniak.ch [84.16.66.175]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B57EF11C for ; Mon, 9 Oct 2023 08:37:09 -0700 (PDT) Received: from smtp-3-0001.mail.infomaniak.ch (unknown [10.4.36.108]) by smtp-2-3000.mail.infomaniak.ch (Postfix) with ESMTPS id 4S43775RMKzMpnst; Mon, 9 Oct 2023 15:37:07 +0000 (UTC) Received: from unknown by smtp-3-0001.mail.infomaniak.ch (Postfix) with ESMTPA id 4S43752y9GzMppB4; Mon, 9 Oct 2023 17:37:05 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=digikod.net; s=20191114; t=1696865827; bh=cckq9ovgURWeuDsq98a+f35kYfa/8F4jXEqh6IzlR3E=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=tCck3znyNdWqN3MzYz+w3ihd5zetMeMTIID7gg9ktvqZXEOS47+8RiDEAiFaYNtg0 K+AzQkBxYmuVtBqcloRyGcuNQ5nhrergMzSc3qsP375Id+fzyhNTZ8kIYXxmA1CFBM On1W6gqkPYtxBCw7BzeLe9zfDCF0u5jN9bC7xTGU= Date: Mon, 9 Oct 2023 17:36:59 +0200 From: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= To: Paul Moore Cc: Casey Schaufler , linux-security-module@vger.kernel.org, jmorris@namei.org, serge@hallyn.com, keescook@chromium.org, john.johansen@canonical.com, penguin-kernel@i-love.sakura.ne.jp, stephen.smalley.work@gmail.com, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org Subject: Re: [PATCH v15 04/11] LSM: syscalls for current process attributes Message-ID: <20231009.MieQu5ou2loo@digikod.net> References: <20230912205658.3432-1-casey@schaufler-ca.com> <20230912205658.3432-5-casey@schaufler-ca.com> <20231003.kooghohS2Aiz@digikod.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Infomaniak-Routing: alpha Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Thu, Oct 05, 2023 at 09:04:34PM -0400, Paul Moore wrote: > On Tue, Oct 3, 2023 at 10:09 AM Mickaël Salaün wrote: > > On Tue, Sep 12, 2023 at 01:56:49PM -0700, Casey Schaufler wrote: > > > Create a system call lsm_get_self_attr() to provide the security > > > module maintained attributes of the current process. > > > Create a system call lsm_set_self_attr() to set a security > > > module maintained attribute of the current process. > > > Historically these attributes have been exposed to user space via > > > entries in procfs under /proc/self/attr. > > > > > > The attribute value is provided in a lsm_ctx structure. The structure > > > identifies the size of the attribute, and the attribute value. The format > > > of the attribute value is defined by the security module. A flags field > > > is included for LSM specific information. It is currently unused and must > > > be 0. The total size of the data, including the lsm_ctx structure and any > > > padding, is maintained as well. > > > > > > struct lsm_ctx { > > > __u64 id; > > > __u64 flags; > > > __u64 len; > > > __u64 ctx_len; > > > __u8 ctx[]; > > > }; > > > > > > Two new LSM hooks are used to interface with the LSMs. > > > security_getselfattr() collects the lsm_ctx values from the > > > LSMs that support the hook, accounting for space requirements. > > > security_setselfattr() identifies which LSM the attribute is > > > intended for and passes it along. > > > > > > Signed-off-by: Casey Schaufler > > > Reviewed-by: Kees Cook > > > Reviewed-by: Serge Hallyn > > > Reviewed-by: John Johansen > > > --- > > > Documentation/userspace-api/lsm.rst | 70 +++++++++++++ > > > include/linux/lsm_hook_defs.h | 4 + > > > include/linux/lsm_hooks.h | 1 + > > > include/linux/security.h | 19 ++++ > > > include/linux/syscalls.h | 5 + > > > include/uapi/linux/lsm.h | 36 +++++++ > > > kernel/sys_ni.c | 2 + > > > security/Makefile | 1 + > > > security/lsm_syscalls.c | 57 +++++++++++ > > > security/security.c | 152 ++++++++++++++++++++++++++++ > > > 10 files changed, 347 insertions(+) > > > create mode 100644 Documentation/userspace-api/lsm.rst > > > create mode 100644 security/lsm_syscalls.c > > ... > > > > diff --git a/security/security.c b/security/security.c > > > index a3489c04b783..0d179750d964 100644 > > > --- a/security/security.c > > > +++ b/security/security.c > > > @@ -3837,6 +3837,158 @@ void security_d_instantiate(struct dentry *dentry, struct inode *inode) > > > } > > > EXPORT_SYMBOL(security_d_instantiate); > > > > > > +/* > > > + * Please keep this in sync with it's counterpart in security/lsm_syscalls.c > > > + */ > > > + > > > +/** > > > + * security_getselfattr - Read an LSM attribute of the current process. > > > + * @attr: which attribute to return > > > + * @uctx: the user-space destination for the information, or NULL > > > + * @size: pointer to the size of space available to receive the data > > > + * @flags: special handling options. LSM_FLAG_SINGLE indicates that only > > > + * attributes associated with the LSM identified in the passed @ctx be > > > + * reported. > > > + * > > > + * A NULL value for @uctx can be used to get both the number of attributes > > > + * and the size of the data. > > > + * > > > + * Returns the number of attributes found on success, negative value > > > + * on error. @size is reset to the total size of the data. > > > + * If @size is insufficient to contain the data -E2BIG is returned. > > > + */ > > > +int security_getselfattr(unsigned int attr, struct lsm_ctx __user *uctx, > > > + size_t __user *size, u32 flags) > > > +{ > > > + struct security_hook_list *hp; > > > + struct lsm_ctx lctx = { .id = LSM_ID_UNDEF, }; > > > + u8 __user *base = (u8 __user *)uctx; > > > + size_t total = 0; > > > + size_t entrysize; > > > + size_t left; > > > + bool toobig = false; > > > + bool single = false; > > > + int count = 0; > > > + int rc; > > > + > > > + if (attr == LSM_ATTR_UNDEF) > > > + return -EINVAL; > > > + if (size == NULL) > > > + return -EINVAL; > > > + if (get_user(left, size)) > > > + return -EFAULT; > > > + > > > + if (flags) { > > > + /* > > > + * Only flag supported is LSM_FLAG_SINGLE > > > + */ > > > + if (flags != LSM_FLAG_SINGLE) > > > + return -EINVAL; > > > + if (uctx && copy_from_user(&lctx, uctx, sizeof(lctx))) > > > > I'm not sure if we should return -EINVAL or -EFAULT when uctx == NULL. > > Because uctx is optional (when LSM_FLAG_SINGLE is not set), I guess > > -EINVAL is OK. > > That's a good point, we should probably the error codes here: if uctx > is NULL in the LSM_FLAG_SINGLE case we should return -EINVAL, if the > copy_from_user() fails we should return -EFAULT. > > > > + return -EFAULT; > > > + /* > > > + * If the LSM ID isn't specified it is an error. > > > + */ > > > + if (lctx.id == LSM_ID_UNDEF) > > > + return -EINVAL; > > > + single = true; > > > + } > > > + > > > + /* > > > + * In the usual case gather all the data from the LSMs. > > > + * In the single case only get the data from the LSM specified. > > > + */ > > > + hlist_for_each_entry(hp, &security_hook_heads.getselfattr, list) { > > > + if (single && lctx.id != hp->lsmid->id) > > > + continue; > > > + entrysize = left; > > > + if (base) > > > + uctx = (struct lsm_ctx __user *)(base + total); > > > + rc = hp->hook.getselfattr(attr, uctx, &entrysize, flags); > > > + if (rc == -EOPNOTSUPP) { > > > + rc = 0; > > > + continue; > > > + } > > > + if (rc == -E2BIG) { > > > + toobig = true; > > > + left = 0; > > > + } else if (rc < 0) > > > + return rc; > > > + else > > > + left -= entrysize; > > > + > > > + total += entrysize; > > > + count += rc; > > > > There is a bug if rc == -E2BIG > > Can you elaborate a bit more on this? Nothing is jumping out at me as > obviously broken... are you talking about @count becoming garbage due > to @rc being equal to -E2BIG? If that is the case it should be okay > since we explicitly return -E2BIG, not @count, if @toobig is true. Indeed, in this case count will not be returned thanks to toobig. I'd suggest to "continue" if rc == -E2BIG (like for -EOPNOTSUPP) to avoid an inconsistent count value, which could bite us one day. > > > > + if (single) > > > + break; > > > + } > > > + if (put_user(total, size)) > > > + return -EFAULT; > > > + if (toobig) > > > + return -E2BIG; > > > + if (count == 0) > > > + return LSM_RET_DEFAULT(getselfattr); > > > + return count; > > > +} > > -- > paul-moore.com