From: Casey Schaufler <casey@schaufler-ca.com>
To: Mimi Zohar <zohar@linux.ibm.com>,
Roberto Sassu <roberto.sassu@huaweicloud.com>,
mark@fasheh.com, jlbec@evilplan.org, joseph.qi@linux.alibaba.com,
dmitry.kasatkin@gmail.com, paul@paul-moore.com,
jmorris@namei.org, serge@hallyn.com,
stephen.smalley.work@gmail.com, eparis@parisplace.org
Cc: ocfs2-devel@oss.oracle.com, reiserfs-devel@vger.kernel.org,
linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
linux-kernel@vger.kernel.org, keescook@chromium.org,
nicolas.bouchinet@clip-os.org,
Roberto Sassu <roberto.sassu@huawei.com>,
casey@schaufler-ca.com
Subject: Re: [PATCH v6 4/6] security: Allow all LSMs to provide xattrs for inode_init_security hook
Date: Tue, 29 Nov 2022 07:39:42 -0800 [thread overview]
Message-ID: <50232f2b-d5ce-1e5a-3f5b-8d3eb53fe1ec@schaufler-ca.com> (raw)
In-Reply-To: <9859294adb0a9b9587ea7fb70a836a312aaf3c69.camel@linux.ibm.com>
On 11/29/2022 3:23 AM, Mimi Zohar wrote:
> On Thu, 2022-11-24 at 09:17 +0100, Roberto Sassu wrote:
>> On Wed, 2022-11-23 at 20:14 -0500, Mimi Zohar wrote:
>>> Hi Roberto,
>>>
>>> On Wed, 2022-11-23 at 16:47 +0100, Roberto Sassu wrote:
>>>> int security_inode_init_security(struct inode *inode, struct inode *dir,
>>>> const struct qstr *qstr,
>>>> const initxattrs initxattrs, void *fs_data)
>>>> {
>>>> - struct xattr new_xattrs[MAX_LSM_EVM_XATTR + 1];
>>>> - struct xattr *lsm_xattr, *evm_xattr, *xattr;
>>>> - int ret;
>>>> + struct security_hook_list *P;
>>>> + struct xattr *new_xattrs;
>>>> + struct xattr *xattr;
>>>> + int ret = -EOPNOTSUPP, num_filled_xattrs = 0;
>>>>
>>>> if (unlikely(IS_PRIVATE(inode)))
>>>> return 0;
>>>>
>>>> + if (!blob_sizes.lbs_xattr)
>>>> + return 0;
>>>> +
>>>> if (!initxattrs)
>>>> return call_int_hook(inode_init_security, -EOPNOTSUPP, inode,
>>>> - dir, qstr, NULL, NULL, NULL);
>>>> - memset(new_xattrs, 0, sizeof(new_xattrs));
>>>> - lsm_xattr = new_xattrs;
>>>> - ret = call_int_hook(inode_init_security, -EOPNOTSUPP, inode, dir, qstr,
>>>> - &lsm_xattr->name,
>>>> - &lsm_xattr->value,
>>>> - &lsm_xattr->value_len);
>>>> - if (ret)
>>>> + dir, qstr, NULL);
>>>> + /* Allocate +1 for EVM and +1 as terminator. */
>>>> + new_xattrs = kcalloc(blob_sizes.lbs_xattr + 2, sizeof(*new_xattrs),
>>>> + GFP_NOFS);
>>>> + if (!new_xattrs)
>>>> + return -ENOMEM;
>>>> +
>>>> + hlist_for_each_entry(P, &security_hook_heads.inode_init_security,
>>>> + list) {
>>>> + ret = P->hook.inode_init_security(inode, dir, qstr, new_xattrs);
>>>> + if (ret && ret != -EOPNOTSUPP)
>>>> + goto out;
>>>> + if (ret == -EOPNOTSUPP)
>>>> + continue;
>>> In this context, -EOPNOTSUPP originally signified that the filesystem
>>> does not support writing xattrs. Writing any xattr would fail.
>>> Returning -ENODATA for no LSM xattr(s) data would seem to be more
>>> appropriate than -EOPNOTSUPP.
>> Hi Mimi
>>
>> I thought about adding new return values. Currently only -EOPNOTSUPP
>> and -ENOMEM are expected as errors.
>>
>> However, changing the conventions would mean revisiting the LSMs code
>> and ensuring that they follow the new conventions.
>>
>> I would be more in favor of not touching it.
> Casey, Paul, any comment?
I don't see value in adding -ENODATA as a value special to
the infrastructure. What would the infrastructure do differently?
The use of -EOPNOTSUPP isn't consistent throughout, and the amount
of "correctness" you get by returning -ENODATA is really small.
>
>>>> + /*
>>>> + * As the number of xattrs reserved by LSMs is not directly
>>>> + * available, directly use the total number blob_sizes.lbs_xattr
>>>> + * to keep the code simple, while being not the most efficient
>>>> + * way.
>>>> + */
>>>> + ret = security_check_compact_filled_xattrs(new_xattrs,
>>>> + blob_sizes.lbs_xattr,
>>>> + &num_filled_xattrs);
>>>> + if (ret < 0) {
>>>> + ret = -ENOMEM;
>>>> + goto out;
>>>> + }
>>>> + }
>>>> +
>>>> + if (!num_filled_xattrs)
>>>> goto out;
>>>>
>>>> - evm_xattr = lsm_xattr + 1;
>>>> - ret = evm_inode_init_security(inode, lsm_xattr, evm_xattr);
>>>> + ret = evm_inode_init_security(inode, new_xattrs,
>>>> + new_xattrs + num_filled_xattrs);
>>>> if (ret)
>>>> goto out;
>>>> ret = initxattrs(inode, new_xattrs, fs_data);
>>>> out:
>>>> for (xattr = new_xattrs; xattr->value != NULL; xattr++)
>>>> kfree(xattr->value);
>>>> + kfree(new_xattrs);
>>>> return (ret == -EOPNOTSUPP) ? 0 : ret;
>>>> }
>>> b
>
next prev parent reply other threads:[~2022-11-29 15:39 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-23 15:47 [PATCH v6 0/6] evm: Do HMAC of multiple per LSM xattrs for new inodes Roberto Sassu
2022-11-23 15:47 ` [PATCH v6 1/6] reiserfs: Switch to security_inode_init_security() Roberto Sassu
2022-11-23 15:47 ` [PATCH v6 2/6] ocfs2: " Roberto Sassu
2022-11-23 15:47 ` [PATCH v6 3/6] security: Remove security_old_inode_init_security() Roberto Sassu
2022-11-23 15:47 ` [PATCH v6 4/6] security: Allow all LSMs to provide xattrs for inode_init_security hook Roberto Sassu
2022-11-23 17:17 ` Casey Schaufler
2022-11-24 7:55 ` Roberto Sassu
2022-11-24 1:14 ` Mimi Zohar
2022-11-24 8:17 ` Roberto Sassu
2022-11-29 11:23 ` Mimi Zohar
2022-11-29 15:39 ` Casey Schaufler [this message]
2022-11-30 21:23 ` Mimi Zohar
2022-11-23 15:47 ` [PATCH v6 5/6] evm: Align evm_inode_init_security() definition with LSM infrastructure Roberto Sassu
2022-11-23 15:47 ` [PATCH v6 6/6] evm: Support multiple LSMs providing an xattr Roberto Sassu
2022-11-23 16:22 ` [PATCH v6 0/6] evm: Do HMAC of multiple per LSM xattrs for new inodes Mimi Zohar
2022-11-23 17:20 ` Casey Schaufler
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