netdev - Re: [PATCH v4 5/20] lsm: Refactor return value of LSM hook inode_copy_up

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Message-ID: <3a8d55e0d41a35a1a3c5d3590240d16b@paul-moore.com>
Date: Thu, 18 Jul 2024 22:08:03 -0400
From: Paul Moore <paul@...l-moore.com>
To: Xu Kuohai <xukuohai@...weicloud.com>, bpf@...r.kernel.org, netdev@...r.kernel.org, linux-security-module@...r.kernel.org, linux-kselftest@...r.kernel.org, linux-integrity@...r.kernel.org, apparmor@...ts.ubuntu.com, selinux@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Matt Bobrowski <mattbobrowski@...gle.com>, 
	Brendan Jackman <jackmanb@...omium.org>, James Morris <jmorris@...ei.org>, 
	"Serge E . Hallyn" <serge@...lyn.com>, Khadija Kamran <kamrankhadijadj@...il.com>, 
	Casey Schaufler <casey@...aufler-ca.com>, Ondrej Mosnacek <omosnace@...hat.com>, 
	Kees Cook <keescook@...omium.org>, John Johansen <john.johansen@...onical.com>, 
	Lukas Bulwahn <lukas.bulwahn@...il.com>, Roberto Sassu <roberto.sassu@...wei.com>, 
	Shung-Hsi Yu <shung-hsi.yu@...e.com>, Edward Cree <ecree.xilinx@...il.com>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, 
	Trond Myklebust <trond.myklebust@...merspace.com>, Anna Schumaker <anna@...nel.org>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Stephen Smalley <stephen.smalley.work@...il.com>
Subject: Re: [PATCH v4 5/20] lsm: Refactor return value of LSM hook  inode_copy_up_xattr

On Jul 11, 2024 Xu Kuohai <xukuohai@...weicloud.com> wrote:
> 
> To be consistent with most LSM hooks, convert the return value of
> hook inode_copy_up_xattr to 0 or a negative error code.
> 
> Before:
> - Hook inode_copy_up_xattr returns 0 when accepting xattr, 1 when
>   discarding xattr, -EOPNOTSUPP if it does not know xattr, or any
>   other negative error code otherwise.
> 
> After:
> - Hook inode_copy_up_xattr returns 0 when accepting xattr, *-ECANCELED*
>   when discarding xattr, -EOPNOTSUPP if it does not know xattr, or
>   any other negative error code otherwise.
> 
> Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
> ---
>  fs/overlayfs/copy_up.c            |  6 +++---
>  security/integrity/evm/evm_main.c |  2 +-
>  security/security.c               | 12 ++++++------
>  security/selinux/hooks.c          |  4 ++--
>  security/smack/smack_lsm.c        |  6 +++---
>  5 files changed, 15 insertions(+), 15 deletions(-)

...

> diff --git a/security/security.c b/security/security.c
> index 26eea8f4cd74..12215ca286af 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2675,18 +2675,18 @@ EXPORT_SYMBOL(security_inode_copy_up);
>   * lower layer to the union/overlay layer.   The caller is responsible for
>   * reading and writing the xattrs, this hook is merely a filter.
>   *
> - * Return: Returns 0 to accept the xattr, 1 to discard the xattr, -EOPNOTSUPP
> - *         if the security module does not know about attribute, or a negative
> - *         error code to abort the copy up.
> + * Return: Returns 0 to accept the xattr, -ECANCELED to discard the xattr,
> + *         -EOPNOTSUPP if the security module does not know about attribute,
> + *         or a negative error code to abort the copy up.
>   */
>  int security_inode_copy_up_xattr(struct dentry *src, const char *name)
>  {
>  	int rc;
>  
>  	/*
> -	 * The implementation can return 0 (accept the xattr), 1 (discard the
> -	 * xattr), -EOPNOTSUPP if it does not know anything about the xattr or
> -	 * any other error code in case of an error.
> +	 * The implementation can return 0 (accept the xattr), -ECANCELED
> +	 * (discard the xattr), -EOPNOTSUPP if it does not know anything
> +	 *  about the xattr or any other error code in case of an error.
>  	 */

Updating the comment here is good, but considering that we also discuss
the return value in the function header comment, I think it might be
better to just remove this comment entirely and leave the function header
comment as the single source.  Duplicated comments/docs tend to fall out
of sync and create confusion.

>  	rc = call_int_hook(inode_copy_up_xattr, src, name);
>  	if (rc != LSM_RET_DEFAULT(inode_copy_up_xattr))


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