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

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Message-ID: <7154a541-d78c-4560-a6de-90340ce23555@huaweicloud.com>
Date: Sat, 13 Jul 2024 16:07:26 +0800
From: Xu Kuohai <xukuohai@...weicloud.com>
To: Simon Horman <horms@...nel.org>
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>,
 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 bpf-next v4 03/20] lsm: Refactor return value of LSM hook
 inode_getsecurity

On 7/12/2024 9:31 PM, Simon Horman wrote:
> 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.
> 
> ...
> 
>

OK, indeed there is no standardization that says ssize_t must be wider than u32.
I'll look into adding overflow checks. Thanks.