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Message-ID: <72b46d0f-75c7-ac18-4984-2bf1d6dad352@schaufler-ca.com>
Date: Wed, 12 Apr 2023 13:29:38 -0700
From: Casey Schaufler <casey@...aufler-ca.com>
To: Roberto Sassu <roberto.sassu@...weicloud.com>, zohar@...ux.ibm.com,
dmitry.kasatkin@...il.com, paul@...l-moore.com, jmorris@...ei.org,
serge@...lyn.com, stephen.smalley.work@...il.com,
eparis@...isplace.org
Cc: reiserfs-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-integrity@...r.kernel.org,
linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
bpf@...r.kernel.org, kpsingh@...nel.org, keescook@...omium.org,
nicolas.bouchinet@...p-os.org,
Roberto Sassu <roberto.sassu@...wei.com>,
Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH] Smack modifications for: security: Allow all LSMs to
provide xattrs for inode_init_security hook
On 4/12/2023 12:22 AM, Roberto Sassu wrote:
> On Tue, 2023-04-11 at 10:54 -0700, Casey Schaufler wrote:
>> On 4/11/2023 10:23 AM, Roberto Sassu wrote:
>>> From: Roberto Sassu <roberto.sassu@...wei.com>
>>>
>>> Very very quick modification. Not tested.
>>>
>>> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
>>> ---
>>> security/smack/smack.h | 2 +-
>>> security/smack/smack_lsm.c | 42 ++++++++++++++++++++------------------
>>> 2 files changed, 23 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/security/smack/smack.h b/security/smack/smack.h
>>> index e2239be7bd6..f00c8498c60 100644
>>> --- a/security/smack/smack.h
>>> +++ b/security/smack/smack.h
>>> @@ -127,7 +127,7 @@ struct task_smack {
>>>
>>> #define SMK_INODE_INSTANT 0x01 /* inode is instantiated */
>>> #define SMK_INODE_TRANSMUTE 0x02 /* directory is transmuting */
>>> -#define SMK_INODE_CHANGED 0x04 /* smack was transmuted */
>>> +#define SMK_INODE_CHANGED 0x04 /* smack was transmuted (unused) */
>> See below ...
>>
>>> #define SMK_INODE_IMPURE 0x08 /* involved in an impure transaction */
>>>
>>> /*
>>> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
>>> index 8392983334b..b43820bdbd0 100644
>>> --- a/security/smack/smack_lsm.c
>>> +++ b/security/smack/smack_lsm.c
>>> @@ -54,12 +54,12 @@
>>>
>>> /*
>>> * Smack uses multiple xattrs.
>>> - * SMACK64 - for access control, SMACK64EXEC - label for the program,
>>> - * SMACK64MMAP - controls library loading,
>>> + * SMACK64 - for access control,
>>> * SMACK64TRANSMUTE - label initialization,
>>> - * Not saved on files - SMACK64IPIN and SMACK64IPOUT
>>> + * Not saved on files - SMACK64IPIN and SMACK64IPOUT,
>>> + * Must be set explicitly - SMACK64EXEC and SMACK64MMAP
>>> */
>>> -#define SMACK_INODE_INIT_XATTRS 4
>>> +#define SMACK_INODE_INIT_XATTRS 2
>>>
>>> #ifdef SMACK_IPV6_PORT_LABELING
>>> static DEFINE_MUTEX(smack_ipv6_lock);
>>> @@ -957,11 +957,11 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
>>> const struct qstr *qstr,
>>> struct xattr *xattrs, int *xattr_count)
>>> {
>>> - struct inode_smack *issp = smack_inode(inode);
>>> struct smack_known *skp = smk_of_current();
>>> struct smack_known *isp = smk_of_inode(inode);
>>> struct smack_known *dsp = smk_of_inode(dir);
>>> struct xattr *xattr = lsm_get_xattr_slot(xattrs, xattr_count);
>>> + struct xattr *xattr2;
>> I'm going to channel Paul and suggest this be xattr_transmute instead of xattr2.
>> It also looks like it could move to be declared in the if clause.
>>
>>> int may;
>>>
>>> if (xattr) {
>>> @@ -979,7 +979,17 @@ static int smack_inode_init_security(struct inode *inode, struct inode *dir,
>>> if (may > 0 && ((may & MAY_TRANSMUTE) != 0) &&
>>> smk_inode_transmutable(dir)) {
>>> isp = dsp;
>>> - issp->smk_flags |= SMK_INODE_CHANGED;
>> I think you need to keep this. More below.
>>
>>> + xattr2 = lsm_get_xattr_slot(xattrs, xattr_count);
>>> + if (xattr2) {
>>> + xattr2->value = kmemdup(TRANS_TRUE,
>>> + TRANS_TRUE_SIZE,
>>> + GFP_NOFS);
>>> + if (xattr2->value == NULL)
>>> + return -ENOMEM;
>>> +
>>> + xattr2->value_len = TRANS_TRUE_SIZE;
>>> + xattr2->name = XATTR_NAME_SMACKTRANSMUTE;
>>> + }
>>> }
>>>
>>> xattr->value = kstrdup(isp->smk_known, GFP_NOFS);
>>> @@ -3512,20 +3522,12 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
>>> * If there is a transmute attribute on the
>>> * directory mark the inode.
>>> */
>>> - if (isp->smk_flags & SMK_INODE_CHANGED) {
>>> - isp->smk_flags &= ~SMK_INODE_CHANGED;
>>> - rc = __vfs_setxattr(&nop_mnt_idmap, dp, inode,
>>> - XATTR_NAME_SMACKTRANSMUTE,
>>> - TRANS_TRUE, TRANS_TRUE_SIZE,
>>> - 0);
>>> - } else {
>>> - rc = __vfs_getxattr(dp, inode,
>>> - XATTR_NAME_SMACKTRANSMUTE, trattr,
>>> - TRANS_TRUE_SIZE);
>>> - if (rc >= 0 && strncmp(trattr, TRANS_TRUE,
>>> - TRANS_TRUE_SIZE) != 0)
>>> - rc = -EINVAL;
>>> - }
>>> + rc = __vfs_getxattr(dp, inode,
>>> + XATTR_NAME_SMACKTRANSMUTE, trattr,
>>> + TRANS_TRUE_SIZE);
>>> + if (rc >= 0 && strncmp(trattr, TRANS_TRUE,
>>> + TRANS_TRUE_SIZE) != 0)
>>> + rc = -EINVAL;
>> Where is the SMACK64_TRANSMUTE attribute going to get set on the file?
>> It's not going to get set in smack_init_inode_security(). The inode will
> Isn't that the purpose of the inode_init_security hook?
No. It initializes the in-memory inode.
> After all LSMs provide one or multiple xattrs, xattrs are going to be
> written to the disk with the initxattr() callback of filesystems.
>
> There is a small mistake above (XATTR_SMACK_TRANSMUTE instead
> of XATTR_NAME_SMACKTRANSMUTE, as we are providing just the suffix).
>
> After fixing that, Smack tests succeed:
It's over a decade since I seriously looked at this code path,
but I'm pretty sure the __vfs_setxattr() call is necessary to get
the attribute written out. With your change the in-memory inode will
get the attribute, but if you reboot it won't be on the directory.
>
> 95 Passed, 0 Failed, 100% Success rate
>
> There was a test failing in dir-transmute.sh, before I fixed the xattr
> name.
>
> Thanks
>
> Roberto
>
>> know it's transmuting, but it won't get to disk without the __vfs_setxattr()
>> here in smack_d_instantiate(). Now, it's been a long time since that code
>> was written, so I could be wrong, but I'm pretty sure about that.
>>
>> I think that you should be fine with the changes in smack_init_inode_security(),
>> and leaving smack_d_instantiate() untouched.
>>
>>> if (rc >= 0)
>>> transflag = SMK_INODE_TRANSMUTE;
>>> }
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