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

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Message-ID: <e70541cb-d239-4b54-a08b-9cf88e43b364@huaweicloud.com>
Date: Sat, 20 Jul 2024 17:28:46 +0800
From: Xu Kuohai <xukuohai@...weicloud.com>
To: Paul Moore <paul@...l-moore.com>, 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, 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>,
 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 7/19/2024 10:08 AM, Paul Moore wrote:
> 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.
>

Got it

>> 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().
>

Sounds great

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