linux-kernel - Re: [PATCH] lsm: simplify security_inode_copy_up

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Message-ID: <c946ad53-15c8-497d-863b-a237e6c4466c@linux.alibaba.com>
Date: Wed, 30 Jul 2025 17:25:50 +0800
From: "tianjia.zhang" <tianjia.zhang@...ux.alibaba.com>
To: Paul Moore <paul@...l-moore.com>, Casey Schaufler <casey@...aufler-ca.com>
Cc: James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>,
 linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lsm: simplify security_inode_copy_up_xattr()



On 7/29/25 11:09 PM, Paul Moore wrote:
> On Tue, Jul 29, 2025 at 10:43 AM Casey Schaufler <casey@...aufler-ca.com> wrote:
>> On 7/29/2025 2:09 AM, Tianjia Zhang wrote:
>>> The implementation of function security_inode_copy_up_xattr can be
>>> simplified to directly call call_int_hook().
>>>
>>> Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
>>> ---
>>>   security/security.c | 8 +-------
>>>   1 file changed, 1 insertion(+), 7 deletions(-)
>>>
>>> diff --git a/security/security.c b/security/security.c
>>> index 596d41818577..a5c2e5a8009f 100644
>>> --- a/security/security.c
>>> +++ b/security/security.c
>>> @@ -2774,13 +2774,7 @@ EXPORT_SYMBOL(security_inode_copy_up);
>>>    */
>>>   int security_inode_copy_up_xattr(struct dentry *src, const char *name)
>>>   {
>>> -     int rc;
>>> -
>>> -     rc = call_int_hook(inode_copy_up_xattr, src, name);
>>> -     if (rc != LSM_RET_DEFAULT(inode_copy_up_xattr))
>>> -             return rc;
>>> -
>>> -     return LSM_RET_DEFAULT(inode_copy_up_xattr);
>>> +     return call_int_hook(inode_copy_up_xattr, src, name);
>>
>> Both the existing code and the proposed change are incorrect.
>> If two LSMs supply the hook, and the first does not recognize
>> the attribute, the second, which might recognize the attribute,
>> will not be called. As SELinux and EVM both supply this hook
>> there may be a real problem here.
> 
> It appears that Smack also supplies a inode_copy_up_xattr() callback
> via smack_inode_copy_up_xattr().
> 
> Someone should double check this logic, but looking at it very
> quickly, it would appear that LSM framework should run the individual
> LSM callbacks in order so long as they return -EOPNOTSUPP, if they do
> not return -EOPNOTSUPP, the return value should be returned to the
> caller without executing any further callbacks.  As a default return
> value, or if all of the LSM callbacks succeed with -EOPNOTSUPP, the
> hook should return -EOPNOTSUPP.
> 
> Tianjia Zhang, would you be able to develop and test a patch for this?
> 

Yes, I will submit a new patch to try to fix this issue. Thanks for your
suggestion.

Cheers,
Tianjia