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 B08EDC001B0 for ; Mon, 7 Aug 2023 13:08:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233846AbjHGNIL (ORCPT ); Mon, 7 Aug 2023 09:08:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55620 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233853AbjHGNIK (ORCPT ); Mon, 7 Aug 2023 09:08:10 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 373D310FD; Mon, 7 Aug 2023 06:08:09 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id BA00561A73; Mon, 7 Aug 2023 13:08:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7FF49C433C8; Mon, 7 Aug 2023 13:08:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1691413688; bh=T4H5FHLaTu/CMH204/FAnov8lc6ZCUi87TDnDHHPTE4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=CRco9KD2M2RT13Q9QDFHqw7O9kx+gb9Xfxmh2X85dVJCyOaKFD6d/qS219QiH46jH fCk6AKnukj8xDtWQZOU2Y/IMZ14PoR6VgFPb+iX39ookD+LXdK9NkS9D4jI6xeP3Ql 281kAbXQJsCXmYSDlwtKYoYTwYzThA/qadNhhVKaDilCJVrADlV5f/1QYueQxzPaIx O5bd2m0pEu6A232+Gzt/JTlXjpg+JwL3yJgLQ0rosx+A8vUZWe9RNcLMqchZ8UD9aL UX7t2E6P0rjgbcYQu0VY9zxIL4aDDjmdlfi/8UwmX7y+o8EFqdKTTIpev+Kgs1NM6d AZV9cjvUh1Mng== Date: Mon, 7 Aug 2023 15:08:01 +0200 From: Christian Brauner To: Jeff Layton Cc: Alexander Viro , Trond Myklebust , Anna Schumaker , Paul Moore , James Morris , "Serge E. Hallyn" , Stephen Smalley , Eric Paris , Casey Schaufler , David Howells , Scott Mayhew , Stephen Smalley , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org Subject: Re: [PATCH v7] vfs, security: Fix automount superblock LSM init problem, preventing NFS sb sharing Message-ID: <20230807-gastdirigent-laufkundschaft-17e681a8e14e@brauner> References: <20230804-master-v7-1-5d4e48407298@kernel.org> <20230805-anrechnen-medien-c639c85ebd42@brauner> <650f7b6ea6b55de4c9cbc791af0da4f800907c21.camel@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <650f7b6ea6b55de4c9cbc791af0da4f800907c21.camel@kernel.org> Precedence: bulk List-ID: On Mon, Aug 07, 2023 at 08:57:03AM -0400, Jeff Layton wrote: > On Sat, 2023-08-05 at 14:43 +0200, Christian Brauner wrote: > > On Fri, Aug 04, 2023 at 12:09:34PM -0400, Jeff Layton wrote: > > > From: David Howells > > > > > > When NFS superblocks are created by automounting, their LSM parameters > > > aren't set in the fs_context struct prior to sget_fc() being called, > > > leading to failure to match existing superblocks. > > > > > > This bug leads to messages like the following appearing in dmesg when > > > fscache is enabled: > > > > > > NFS: Cache volume key already in use (nfs,4.2,2,108,106a8c0,1,,,,100000,100000,2ee,3a98,1d4c,3a98,1) > > > > > > Fix this by adding a new LSM hook to load fc->security for submount > > > creation when alloc_fs_context() is creating the fs_context for it. > > > > > > Signed-off-by: David Howells > > > Signed-off-by: Jeff Layton > > > Fixes: 9bc61ab18b1d ("vfs: Introduce fs_context, switch vfs_kern_mount() to it.") > > > Fixes: 779df6a5480f ("NFS: Ensure security label is set for root inode) > > > Tested-by: Jeff Layton > > > Reviewed-by: Jeff Layton > > > Acked-by: Casey Schaufler > > > Acked-by: "Christian Brauner (Microsoft)" > > > Link: https://lore.kernel.org/r/165962680944.3334508.6610023900349142034.stgit@warthog.procyon.org.uk/ # v1 > > > Link: https://lore.kernel.org/r/165962729225.3357250.14350728846471527137.stgit@warthog.procyon.org.uk/ # v2 > > > Link: https://lore.kernel.org/r/165970659095.2812394.6868894171102318796.stgit@warthog.procyon.org.uk/ # v3 > > > Link: https://lore.kernel.org/r/166133579016.3678898.6283195019480567275.stgit@warthog.procyon.org.uk/ # v4 > > > Link: https://lore.kernel.org/r/217595.1662033775@warthog.procyon.org.uk/ # v5 > > > --- > > > ver #7) > > > - Drop lsm_set boolean > > > - Link to v6: https://lore.kernel.org/r/20230802-master-v6-1-45d48299168b@kernel.org > > > > > > ver #6) > > > - Rebase onto v6.5.0-rc4 > > > > > > ver #5) > > > - Removed unused variable. > > > - Only allocate smack_mnt_opts if we're dealing with a submount. > > > > > > ver #4) > > > - When doing a FOR_SUBMOUNT mount, don't set the root label in SELinux or > > > Smack. > > > > > > ver #3) > > > - Made LSM parameter extraction dependent on fc->purpose == > > > FS_CONTEXT_FOR_SUBMOUNT. Shouldn't happen on FOR_RECONFIGURE. > > > > > > ver #2) > > > - Added Smack support > > > - Made LSM parameter extraction dependent on reference != NULL. > > > --- > > > fs/fs_context.c | 4 ++++ > > > include/linux/lsm_hook_defs.h | 1 + > > > include/linux/security.h | 6 +++++ > > > security/security.c | 14 +++++++++++ > > > security/selinux/hooks.c | 25 ++++++++++++++++++++ > > > security/smack/smack_lsm.c | 54 +++++++++++++++++++++++++++++++++++++++++++ > > > 6 files changed, 104 insertions(+) > > > > > > diff --git a/fs/fs_context.c b/fs/fs_context.c > > > index 851214d1d013..a523aea956c4 100644 > > > --- a/fs/fs_context.c > > > +++ b/fs/fs_context.c > > > @@ -282,6 +282,10 @@ static struct fs_context *alloc_fs_context(struct file_system_type *fs_type, > > > break; > > > } > > > > > > + ret = security_fs_context_init(fc, reference); > > > + if (ret < 0) > > > + goto err_fc; > > > + > > > /* TODO: Make all filesystems support this unconditionally */ > > > init_fs_context = fc->fs_type->init_fs_context; > > > if (!init_fs_context) > > > diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h > > > index 7308a1a7599b..7ce3550154b1 100644 > > > --- a/include/linux/lsm_hook_defs.h > > > +++ b/include/linux/lsm_hook_defs.h > > > @@ -54,6 +54,7 @@ LSM_HOOK(int, 0, bprm_creds_from_file, struct linux_binprm *bprm, struct file *f > > > LSM_HOOK(int, 0, bprm_check_security, struct linux_binprm *bprm) > > > LSM_HOOK(void, LSM_RET_VOID, bprm_committing_creds, struct linux_binprm *bprm) > > > LSM_HOOK(void, LSM_RET_VOID, bprm_committed_creds, struct linux_binprm *bprm) > > > +LSM_HOOK(int, 0, fs_context_init, struct fs_context *fc, struct dentry *reference) > > > LSM_HOOK(int, 0, fs_context_dup, struct fs_context *fc, > > > struct fs_context *src_sc) > > > LSM_HOOK(int, -ENOPARAM, fs_context_parse_param, struct fs_context *fc, > > > diff --git a/include/linux/security.h b/include/linux/security.h > > > index 32828502f09e..61fda06fac9d 100644 > > > --- a/include/linux/security.h > > > +++ b/include/linux/security.h > > > @@ -293,6 +293,7 @@ int security_bprm_creds_from_file(struct linux_binprm *bprm, struct file *file); > > > int security_bprm_check(struct linux_binprm *bprm); > > > void security_bprm_committing_creds(struct linux_binprm *bprm); > > > void security_bprm_committed_creds(struct linux_binprm *bprm); > > > +int security_fs_context_init(struct fs_context *fc, struct dentry *reference); > > > int security_fs_context_dup(struct fs_context *fc, struct fs_context *src_fc); > > > int security_fs_context_parse_param(struct fs_context *fc, struct fs_parameter *param); > > > int security_sb_alloc(struct super_block *sb); > > > @@ -629,6 +630,11 @@ static inline void security_bprm_committed_creds(struct linux_binprm *bprm) > > > { > > > } > > > > > > +static inline int security_fs_context_init(struct fs_context *fc, > > > + struct dentry *reference) > > > > I think that's the wrong way of doing this hook. The security hook > > really doesn't belong into alloc_fs_context(). > > > > I think what we want is a dedicated helper similar to vfs_dup_context(): > > > > // Only pass the superblock. There's no need for the dentry. I would > > // avoid even passing fs_context but if that's preferred then sure. > > security_fs_context_submount(struct fs_context *fc, const struct super_block *sb) > > > > vfs_submount_fs_context(struct file_system_type *fs_type, struct dentry *reference) > > { > > fc = fs_context_for_submount(fs_type, reference); > > > > security_fs_context_for_submount(fc, reference->d_sb); > > } > > > > This automatically ensures it's only called for submounts, the LSM > > doesn't need to care about fc->purpose and this isn't called > > in a pure allocation function for all allocation calls. > > > > The we should switch all callers over to that new helper and unexport > > that fs_context_for_submount() thing completely. Yes, that's more work > > but that's the correct thing to do. And we need to audit fuse, cifs, > > afs, and nfs anyway that they work fine with the new security hook.* > > > > It's the same prototype. We could just move the hook call to the end of > fs_context_for_submount, and that would be less churn for its callers. If you just add it into fs_context_for_submount() after the allocation and then leave that as first class citizen it's fine ofc. It's the same result as what I mentioned earlier. We just shouldn't put generic hooks in an allocation function that allocates different types of filesystem contexts. I prefer to have them as targeted as possible and also avoid unnecessary trips into the LSM layer. > Or were you wanting to do that to make this a more gradual changeover > for some reason? No, I think it's fine if you switch it all in one go. I just don't know if fuse/virtiofs submounts expect an selinux context to be bestowed upon them.