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Message-ID: <13f7542f-4039-47a8-abde-45a702b85718@schaufler-ca.com>
Date: Mon, 20 Nov 2023 10:03:59 -0800
From: Casey Schaufler <casey@...aufler-ca.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,
zohar@...ux.ibm.com, dmitry.kasatkin@...il.com,
dhowells@...hat.com, jarkko@...nel.org,
stephen.smalley.work@...il.com, eparis@...isplace.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, Roberto Sassu <roberto.sassu@...wei.com>,
Stefan Berger <stefanb@...ux.ibm.com>,
Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v5 11/23] security: Introduce inode_post_removexattr hook
On 11/20/2023 9:31 AM, Roberto Sassu wrote:
> On Tue, 2023-11-07 at 09:33 -0800, Casey Schaufler wrote:
>> On 11/7/2023 5:40 AM, Roberto Sassu wrote:
>>> From: Roberto Sassu <roberto.sassu@...wei.com>
>>>
>>> In preparation for moving IMA and EVM to the LSM infrastructure, introduce
>>> the inode_post_removexattr hook.
>>>
>>> At inode_removexattr hook, EVM verifies the file's existing HMAC value. At
>>> inode_post_removexattr, EVM re-calculates the file's HMAC with the passed
>>> xattr removed and other file metadata.
>>>
>>> Other LSMs could similarly take some action after successful xattr removal.
>>>
>>> The new hook cannot return an error and cannot cause the operation to be
>>> reverted.
>>>
>>> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
>>> Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
>>> Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
>>> ---
>>> fs/xattr.c | 9 +++++----
>>> include/linux/lsm_hook_defs.h | 2 ++
>>> include/linux/security.h | 5 +++++
>>> security/security.c | 14 ++++++++++++++
>>> 4 files changed, 26 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/fs/xattr.c b/fs/xattr.c
>>> index 09d927603433..84a4aa566c02 100644
>>> --- a/fs/xattr.c
>>> +++ b/fs/xattr.c
>>> @@ -552,11 +552,12 @@ __vfs_removexattr_locked(struct mnt_idmap *idmap,
>>> goto out;
>>>
>>> error = __vfs_removexattr(idmap, dentry, name);
>>> + if (error)
>>> + goto out;
>> Shouldn't this be simply "return error" rather than a goto to nothing
>> but "return error"?
> I got a review from Andrew Morton. His argument seems convincing, that
> having less return places makes the code easier to handle.
That was in a case where you did more than just "return". Nonetheless,
I think it's a matter of style that's not worth debating. Do as you will.
>
> Thanks
>
> Roberto
>
>>> - if (!error) {
>>> - fsnotify_xattr(dentry);
>>> - evm_inode_post_removexattr(dentry, name);
>>> - }
>>> + fsnotify_xattr(dentry);
>>> + security_inode_post_removexattr(dentry, name);
>>> + evm_inode_post_removexattr(dentry, name);
>>>
>>> out:
>>> return error;
>>> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
>>> index 67410e085205..88452e45025c 100644
>>> --- a/include/linux/lsm_hook_defs.h
>>> +++ b/include/linux/lsm_hook_defs.h
>>> @@ -149,6 +149,8 @@ LSM_HOOK(int, 0, inode_getxattr, struct dentry *dentry, const char *name)
>>> LSM_HOOK(int, 0, inode_listxattr, struct dentry *dentry)
>>> LSM_HOOK(int, 0, inode_removexattr, struct mnt_idmap *idmap,
>>> struct dentry *dentry, const char *name)
>>> +LSM_HOOK(void, LSM_RET_VOID, inode_post_removexattr, struct dentry *dentry,
>>> + const char *name)
>>> LSM_HOOK(int, 0, inode_set_acl, struct mnt_idmap *idmap,
>>> struct dentry *dentry, const char *acl_name, struct posix_acl *kacl)
>>> LSM_HOOK(int, 0, inode_get_acl, struct mnt_idmap *idmap,
>>> diff --git a/include/linux/security.h b/include/linux/security.h
>>> index 664df46b22a9..922ea7709bae 100644
>>> --- a/include/linux/security.h
>>> +++ b/include/linux/security.h
>>> @@ -380,6 +380,7 @@ int security_inode_getxattr(struct dentry *dentry, const char *name);
>>> int security_inode_listxattr(struct dentry *dentry);
>>> int security_inode_removexattr(struct mnt_idmap *idmap,
>>> struct dentry *dentry, const char *name);
>>> +void security_inode_post_removexattr(struct dentry *dentry, const char *name);
>>> int security_inode_need_killpriv(struct dentry *dentry);
>>> int security_inode_killpriv(struct mnt_idmap *idmap, struct dentry *dentry);
>>> int security_inode_getsecurity(struct mnt_idmap *idmap,
>>> @@ -940,6 +941,10 @@ static inline int security_inode_removexattr(struct mnt_idmap *idmap,
>>> return cap_inode_removexattr(idmap, dentry, name);
>>> }
>>>
>>> +static inline void security_inode_post_removexattr(struct dentry *dentry,
>>> + const char *name)
>>> +{ }
>>> +
>>> static inline int security_inode_need_killpriv(struct dentry *dentry)
>>> {
>>> return cap_inode_need_killpriv(dentry);
>>> diff --git a/security/security.c b/security/security.c
>>> index ce3bc7642e18..8aa6e9f316dd 100644
>>> --- a/security/security.c
>>> +++ b/security/security.c
>>> @@ -2452,6 +2452,20 @@ int security_inode_removexattr(struct mnt_idmap *idmap,
>>> return evm_inode_removexattr(idmap, dentry, name);
>>> }
>>>
>>> +/**
>>> + * security_inode_post_removexattr() - Update the inode after a removexattr op
>>> + * @dentry: file
>>> + * @name: xattr name
>>> + *
>>> + * Update the inode after a successful removexattr operation.
>>> + */
>>> +void security_inode_post_removexattr(struct dentry *dentry, const char *name)
>>> +{
>>> + if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
>>> + return;
>>> + call_void_hook(inode_post_removexattr, dentry, name);
>>> +}
>>> +
>>> /**
>>> * security_inode_need_killpriv() - Check if security_inode_killpriv() required
>>> * @dentry: associated dentry
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