netdev - Re: [PATCH v4 3/20] lsm: Refactor return value of LSM hook inode

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Message-ID: <bae9304f6fd9ac9536f709a990085119@paul-moore.com>
Date: Thu, 18 Jul 2024 22:08:01 -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 3/20] lsm: Refactor return value of LSM hook  inode_getsecurity

On Jul 11, 2024 Xu Kuohai <xukuohai@...weicloud.com> wrote:
> 
> To be consistent with most LSM hooks, convert the return value of
> hook inode_getsecurity to 0 or a negative error code.
> 
> Before:
> - Hook inode_getsecurity returns size of buffer on success or a
>   negative error code on failure.
> 
> After:
> - Hook inode_getsecurity returns 0 on success or a negative error
>   code on failure. An output parameter @len is introduced to hold
>   the buffer size on success.
> 
> Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
> ---
>  fs/xattr.c                    | 19 ++++++++++---------
>  include/linux/lsm_hook_defs.h |  3 ++-
>  include/linux/security.h      | 12 ++++++------
>  security/commoncap.c          |  9 ++++++---
>  security/security.c           | 11 ++++++-----
>  security/selinux/hooks.c      | 16 ++++++----------
>  security/smack/smack_lsm.c    | 14 +++++++-------
>  7 files changed, 43 insertions(+), 41 deletions(-)

Aside from Simon's concern over variable types, I saw a few other issues
when looking at this patch (below).

> diff --git a/security/commoncap.c b/security/commoncap.c
> index 17d6188d22cf..ff82e2ab6f8f 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -485,7 +485,10 @@ int cap_inode_getsecurity(struct mnt_idmap *idmap,
>  	}
>  out_free:
>  	kfree(tmpbuf);
> -	return size;
> +	if (size < 0)
> +		return size;
> +	*len = size;
> +	return 0;
>  }

We should do a better job converting cap_inode_getsecurity(), create a
new local variable, e.g. 'int error', and use it to store and return the
error code instead of reusing @size.  I understand that what you've done
is easier, but I'd prefer to see it done properly.

> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 9cd5a8f1f6a3..70792bba24d9 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3407,7 +3407,7 @@ static int selinux_path_notify(const struct path *path, u64 mask,
>   */
>  static int selinux_inode_getsecurity(struct mnt_idmap *idmap,
>  				     struct inode *inode, const char *name,
> -				     void **buffer, bool alloc)
> +				     bool alloc, void **buffer, u32 *len)
>  {
>  	u32 size;
>  	int error;
> @@ -3440,14 +3440,14 @@ static int selinux_inode_getsecurity(struct mnt_idmap *idmap,
>  						&context, &size);
>  	if (error)
>  		return error;
> -	error = size;
> +	*len = size;

Depending on how you choose to resolve the variable type issue, you may
be able to pass @len directly to security_sid_to_context().

>  	if (alloc) {
>  		*buffer = context;
>  		goto out_nofree;
>  	}
>  	kfree(context);
>  out_nofree:
> -	return error;
> +	return 0;
>  }


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