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 BA768C001DB for ; Mon, 7 Aug 2023 12:57:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233562AbjHGM5J (ORCPT ); Mon, 7 Aug 2023 08:57:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51260 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232548AbjHGM5J (ORCPT ); Mon, 7 Aug 2023 08:57:09 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7B1DE10FD; Mon, 7 Aug 2023 05:57:07 -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 93BF5619EC; Mon, 7 Aug 2023 12:57:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 69D66C433C9; Mon, 7 Aug 2023 12:57:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1691413026; bh=mt1uuFOc8AlyTQ1K8cBuzB7Csp9E0a8Jlb1PTdNlCp0=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=jAy5x1jASO3bVRPC78HEg0wHowcZoXtyllawrTdBEwQgceCCOovenUYMXV4Ph/dRD RBukby2R3Ud+sLX3uZv7UGsK1zfOSPF9+Bu/RBqOnc3jYbCDWk/BoGxPgA/2r3r6zw zgFILbbA7pRWxUNxWgrHvykIc4rpB74nklYVAefu15qE1grPgMC9I1dNFH1O3azBJL B0EMkt/MfnUWT/Vnd7j37m2uoiMZBR13TPOCn7veRdC7bU/OWsOPxK9GlD6nWfkcGl b2HU9SxG+xncyjJxEhNeQi+7jFjsg2u7frLL+YMTW2c3t6s5fPgfdKU6A2xhd8GrGi M4dW1B0/4b1ig== Message-ID: <650f7b6ea6b55de4c9cbc791af0da4f800907c21.camel@kernel.org> Subject: Re: [PATCH v7] vfs, security: Fix automount superblock LSM init problem, preventing NFS sb sharing From: Jeff Layton To: Christian Brauner 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 Date: Mon, 07 Aug 2023 08:57:03 -0400 In-Reply-To: <20230805-anrechnen-medien-c639c85ebd42@brauner> References: <20230804-master-v7-1-5d4e48407298@kernel.org> <20230805-anrechnen-medien-c639c85ebd42@brauner> Content-Type: text/plain; charset="ISO-8859-15" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.48.4 (3.48.4-1.fc38) MIME-Version: 1.0 Precedence: bulk List-ID: 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 > >=20 > > 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. > >=20 > > This bug leads to messages like the following appearing in dmesg when > > fscache is enabled: > >=20 > > NFS: Cache volume key already in use (nfs,4.2,2,108,106a8c0,1,,,,10= 0000,100000,2ee,3a98,1d4c,3a98,1) > >=20 > > 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. > >=20 > > 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/165962680944.3334508.661002390034914203= 4.stgit@warthog.procyon.org.uk/ # v1 > > Link: https://lore.kernel.org/r/165962729225.3357250.143507288464715271= 37.stgit@warthog.procyon.org.uk/ # v2 > > Link: https://lore.kernel.org/r/165970659095.2812394.686889417110231879= 6.stgit@warthog.procyon.org.uk/ # v3 > > Link: https://lore.kernel.org/r/166133579016.3678898.628319501948056727= 5.stgit@warthog.procyon.org.uk/ # v4 > > Link: https://lore.kernel.org/r/217595.1662033775@warthog.procyon.org.u= k/ # v5 > > --- > > ver #7) > > - Drop lsm_set boolean > > - Link to v6: https://lore.kernel.org/r/20230802-master-v6-1-45d482991= 68b@kernel.org > >=20 > > ver #6) > > - Rebase onto v6.5.0-rc4 > >=20 > > ver #5) > > - Removed unused variable. > > - Only allocate smack_mnt_opts if we're dealing with a submount. > >=20 > > ver #4) > > - When doing a FOR_SUBMOUNT mount, don't set the root label in SELinux= or > > Smack. > >=20 > > ver #3) > > - Made LSM parameter extraction dependent on fc->purpose =3D=3D > > FS_CONTEXT_FOR_SUBMOUNT. Shouldn't happen on FOR_RECONFIGURE. > >=20 > > ver #2) > > - Added Smack support > > - Made LSM parameter extraction dependent on reference !=3D 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(+) > >=20 > > 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; > > } > > =20 > > + ret =3D security_fs_context_init(fc, reference); > > + if (ret < 0) > > + goto err_fc; > > + > > /* TODO: Make all filesystems support this unconditionally */ > > init_fs_context =3D fc->fs_type->init_fs_context; > > if (!init_fs_context) > > diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_def= s.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_b= inprm *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_binpr= m *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_binp= rm *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 *ref= erence); > > 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_p= arameter *param); > > int security_sb_alloc(struct super_block *sb); > > @@ -629,6 +630,11 @@ static inline void security_bprm_committed_creds(s= truct linux_binprm *bprm) > > { > > } > > =20 > > +static inline int security_fs_context_init(struct fs_context *fc, > > + struct dentry *reference) >=20 > I think that's the wrong way of doing this hook. The security hook > really doesn't belong into alloc_fs_context(). >=20 > I think what we want is a dedicated helper similar to vfs_dup_context(): >=20 > // 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_bl= ock *sb) >=20 > vfs_submount_fs_context(struct file_system_type *fs_type, struct dentry *= reference) > { > fc =3D fs_context_for_submount(fs_type, reference); >=20 > security_fs_context_for_submount(fc, reference->d_sb); > } >=20 > 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. >=20 > 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.* >=20 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. Or were you wanting to do that to make this a more gradual changeover for some reason? I will rework the security hook to take a sb pointer instead though. >=20 > [1]: If really needed, then any additional fs specific work that needs > to be done during submount allocation should probably probably be > done in a new callback. >=20 > struct fs_context_operations { > void (*free)(struct fs_context *fc); > int (*dup)(struct fs_context *fc, struct fs_context *src_fc); > + int (*submount)(struct fs_context *fc, const struct super_blo= ck *sb); --=20 Jeff Layton