linux-kernel - Re: [PATCH v8 21/24] evm: Move to LSM infrastructure

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Message-ID: <b03e68e9fa1803d6b2cc7a2c0260f78a05a4d88e.camel@linux.ibm.com>
Date: Tue, 26 Dec 2023 17:13:59 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Roberto Sassu <roberto.sassu@...weicloud.com>, viro@...iv.linux.org.uk,
        brauner@...nel.org, chuck.lever@...cle.com, jlayton@...nel.org,
        neilb@...e.de, kolga@...app.com, Dai.Ngo@...cle.com, tom@...pey.com,
        paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com,
        dmitry.kasatkin@...il.com, dhowells@...hat.com, jarkko@...nel.org,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        casey@...aufler-ca.com, shuah@...nel.org, mic@...ikod.net
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        selinux@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Roberto Sassu
	 <roberto.sassu@...wei.com>
Subject: Re: [PATCH v8 21/24] evm: Move to LSM infrastructure

On Thu, 2023-12-14 at 18:08 +0100, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@...wei.com>
> 
> As for IMA, move hardcoded EVM function calls from various places in the
> kernel to the LSM infrastructure, by introducing a new LSM named 'evm'
> (last and always enabled like 'ima'). The order in the Makefile ensures
> that 'evm' hooks are executed after 'ima' ones.
> 
> Make EVM functions as static (except for evm_inode_init_security(), which
> is exported), and register them as hook implementations in init_evm_lsm().
> 
> Unlike before (see commit to move IMA to the LSM infrastructure),
> evm_inode_post_setattr(), evm_inode_post_set_acl(),
> evm_inode_post_remove_acl(), and evm_inode_post_removexattr() are not
> executed for private inodes.
> 

Missing is a comment on moving the inline function definitions -
evm_inode_remove_acl(), evm_inode_post_remove_acl(), and
evm_inode_post_set_acl() - to evm_main.c.

> Finally, add the LSM_ID_EVM case in lsm_list_modules_test.c
> 
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> ---

[...] 
> @@ -2307,9 +2299,7 @@ int security_inode_setxattr(struct mnt_idmap *idmap,
>  
>  	if (ret == 1)
>  		ret = cap_inode_setxattr(dentry, name, value, size, flags);
> -	if (ret)
> -		return ret;
> -	return evm_inode_setxattr(idmap, dentry, name, value, size, flags);
> +	return ret;
>  }

Even though capability will be called after EVM, it doesn't make a
difference in this instance.

[...]

>  /**
> @@ -2493,9 +2472,7 @@ int security_inode_removexattr(struct mnt_idmap *idmap,
>  	ret = call_int_hook(inode_removexattr, 1, idmap, dentry, name);
>  	if (ret == 1)
>  		ret = cap_inode_removexattr(idmap, dentry, name);
> -	if (ret)
> -		return ret;
> -	return evm_inode_removexattr(idmap, dentry, name);
> +	return ret;
>  }

'security.capability' is one of the EVM protected xattrs.  As
capability isn't an LSM, it will now be called after EVM, which is a
problem.

-- 
thanks,

Mimi