linux-kernel - Re: [PATCH v5 23/23] integrity: Switch from rbtree to LSM-managed blob for integrity_iint

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 13 Dec 2023 11:45:54 +0100
From:   Roberto Sassu <roberto.sassu@...weicloud.com>
To:     Paul Moore <paul@...l-moore.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, jmorris@...ei.org, serge@...lyn.com,
        zohar@...ux.ibm.com, dmitry.kasatkin@...il.com,
        dhowells@...hat.com, jarkko@...nel.org,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        casey@...aufler-ca.com, 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, Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [PATCH v5 23/23] integrity: Switch from rbtree to LSM-managed
 blob for integrity_iint_cache

On 17.11.23 21:57, Paul Moore wrote:
> On Nov  7, 2023 Roberto Sassu <roberto.sassu@...weicloud.com> wrote:
>>
>> Before the security field of kernel objects could be shared among LSMs with
>> the LSM stacking feature, IMA and EVM had to rely on an alternative storage
>> of inode metadata. The association between inode metadata and inode is
>> maintained through an rbtree.
>>
>> Because of this alternative storage mechanism, there was no need to use
>> disjoint inode metadata, so IMA and EVM today still share them.
>>
>> With the reservation mechanism offered by the LSM infrastructure, the
>> rbtree is no longer necessary, as each LSM could reserve a space in the
>> security blob for each inode. However, since IMA and EVM share the
>> inode metadata, they cannot directly reserve the space for them.
>>
>> Instead, request from the 'integrity' LSM a space in the security blob for
>> the pointer of inode metadata (integrity_iint_cache structure). The other
>> reason for keeping the 'integrity' LSM is to preserve the original ordering
>> of IMA and EVM functions as when they were hardcoded.
>>
>> Prefer reserving space for a pointer to allocating the integrity_iint_cache
>> structure directly, as IMA would require it only for a subset of inodes.
>> Always allocating it would cause a waste of memory.
>>
>> Introduce two primitives for getting and setting the pointer of
>> integrity_iint_cache in the security blob, respectively
>> integrity_inode_get_iint() and integrity_inode_set_iint(). This would make
>> the code more understandable, as they directly replace rbtree operations.
>>
>> Locking is not needed, as access to inode metadata is not shared, it is per
>> inode.
>>
>> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
>> Reviewed-by: Casey Schaufler <casey@...aufler-ca.com>
>> Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
>> ---
>>   security/integrity/iint.c      | 71 +++++-----------------------------
>>   security/integrity/integrity.h | 20 +++++++++-
>>   2 files changed, 29 insertions(+), 62 deletions(-)
>>
>> diff --git a/security/integrity/iint.c b/security/integrity/iint.c
>> index 882fde2a2607..a5edd3c70784 100644
>> --- a/security/integrity/iint.c
>> +++ b/security/integrity/iint.c
>> @@ -231,6 +175,10 @@ static int __init integrity_lsm_init(void)
>>   	return 0;
>>   }
>>   
>> +struct lsm_blob_sizes integrity_blob_sizes __ro_after_init = {
>> +	.lbs_inode = sizeof(struct integrity_iint_cache *),
>> +};
> 
> I'll admit that I'm likely missing an important detail, but is there
> a reason why you couldn't stash the integrity_iint_cache struct
> directly in the inode's security blob instead of the pointer?  For
> example:
> 
>    struct lsm_blob_sizes ... = {
>      .lbs_inode = sizeof(struct integrity_iint_cache),
>    };
> 
>    struct integrity_iint_cache *integrity_inode_get(inode)
>    {
>      if (unlikely(!inode->isecurity))
>        return NULL;

Ok, this caught my attention...

I see that selinux_inode() has it, but smack_inode() doesn't.

Some Smack code assumes that the inode security blob is always non-NULL:

static void init_inode_smack(struct inode *inode, struct smack_known *skp)
{
	struct inode_smack *isp = smack_inode(inode);

	isp->smk_inode = skp;
	isp->smk_flags = 0;
}


Is that intended? Should I add the check?

Thanks

Roberto

>      return inode->i_security + integrity_blob_sizes.lbs_inode;
>    }
> 
> --
> paul-moore.com