netdev - Re: [PATCH bpf-next v4 03/20] lsm: Refactor return value of LSM hook inode

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Message-ID: <20240712133141.GB120802@kernel.org>
Date: Fri, 12 Jul 2024 14:31:41 +0100
From: Simon Horman <horms@...nel.org>
To: Xu Kuohai <xukuohai@...weicloud.com>
Cc: 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,
	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>,
	Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
	"Serge E . Hallyn" <serge@...lyn.com>,
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	Casey Schaufler <casey@...aufler-ca.com>,
	Ondrej Mosnacek <omosnace@...hat.com>,
	Kees Cook <keescook@...omium.org>,
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	Lukas Bulwahn <lukas.bulwahn@...il.com>,
	Roberto Sassu <roberto.sassu@...wei.com>,
	Shung-Hsi Yu <shung-hsi.yu@...e.com>,
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	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Trond Myklebust <trond.myklebust@...merspace.com>,
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	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 bpf-next v4 03/20] lsm: Refactor return value of LSM hook
 inode_getsecurity

On Thu, Jul 11, 2024 at 07:18:51PM +0800, Xu Kuohai wrote:
> From: Xu Kuohai <xukuohai@...wei.com>
> 
> 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(-)
> 
> diff --git a/fs/xattr.c b/fs/xattr.c
> index f8b643f91a98..f4e3bedf7272 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -339,27 +339,28 @@ xattr_getsecurity(struct mnt_idmap *idmap, struct inode *inode,
>  		  const char *name, void *value, size_t size)
>  {
>  	void *buffer = NULL;
> -	ssize_t len;
> +	int error;
> +	u32 len;
>  
>  	if (!value || !size) {
> -		len = security_inode_getsecurity(idmap, inode, name,
> -						 &buffer, false);
> +		error = security_inode_getsecurity(idmap, inode, name,
> +						   false, &buffer, &len);
>  		goto out_noalloc;
>  	}
>  
> -	len = security_inode_getsecurity(idmap, inode, name, &buffer,
> -					 true);
> -	if (len < 0)
> -		return len;
> +	error = security_inode_getsecurity(idmap, inode, name, true,
> +					   &buffer, &len);
> +	if (error)
> +		return error;
>  	if (size < len) {
> -		len = -ERANGE;
> +		error = -ERANGE;
>  		goto out;
>  	}
>  	memcpy(value, buffer, len);
>  out:
>  	kfree(buffer);
>  out_noalloc:
> -	return len;
> +	return error < 0 ? error : len;

Hi Xu Kuohai,

len is an unsigned 32-bit entity, but the return type of this function
is an unsigned value (ssize_t). So in theory, if len is very large,
a negative error value error will be returned.

>  }

Similarly for the handling of nattr in lsm_get_self_attr in
lsm_syscalls.c in a subsequent patch.

Flagged by Smatch.

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