Re: [PATCH v7 2/6] ocfs2: Switch to security_inode_init_security()

[Mimi Zohar <zohar@linux.ibm.com>]

On Thu, 2022-12-01 at 11:41 +0100, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@huawei.com>
> 
> In preparation for removing security_old_inode_init_security(), switch to
> security_inode_init_security().
> 
> Extend the existing ocfs2_initxattrs() to take the
> ocfs2_security_xattr_info structure from fs_info, and populate the
> name/value/len triple with the first xattr provided by LSMs.
> 
> As fs_info was not used before, ocfs2_initxattrs() can now handle the case
> of replicating the behavior of security_old_inode_init_security(), i.e.
> just obtaining the xattr, in addition to setting all xattrs provided by
> LSMs.
> 
> Supporting multiple xattrs is not currently supported where
> security_old_inode_init_security() was called (mknod, symlink), as it
> requires non-trivial changes that can be done at a later time. Like for
> reiserfs, even if EVM is invoked, it will not provide an xattr (if it is
> not the first to set it, its xattr will be discarded; if it is the first,
> it does not have xattrs to calculate the HMAC on).
> 
> Finally, modify the handling of the return value from
> ocfs2_init_security_get(). As security_inode_init_security() does not
> return -EOPNOTSUPP, remove this case and directly handle the error if the
> return value is not zero.
> 
> However, the previous case of receiving -EOPNOTSUPP should be still
> taken into account, as security_inode_init_security() could return zero
> without setting xattrs and ocfs2 would consider it as if the xattr was set.
> 
> Instead, if security_inode_init_security() returned zero, look at the xattr
> if it was set, and behave accordingly, i.e. set si->enable to zero to
> notify to the functions following ocfs2_init_security_get() that the xattr
> is not available (same as if security_old_inode_init_security() returned
> -EOPNOTSUPP).
> 
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>

My previous review missed a couple of concerns.

> ---
>  fs/ocfs2/namei.c | 18 ++++++------------
>  fs/ocfs2/xattr.c | 30 ++++++++++++++++++++++++++----
>  2 files changed, 32 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c
> index 05f32989bad6..55fba81cd2d1 100644
> --- a/fs/ocfs2/namei.c
> +++ b/fs/ocfs2/namei.c
> @@ -242,6 +242,7 @@ static int ocfs2_mknod(struct user_namespace *mnt_userns,
>  	int want_meta = 0;
>  	int xattr_credits = 0;
>  	struct ocfs2_security_xattr_info si = {
> +		.name = NULL,
>  		.enable = 1,
>  	};
>  	int did_quota_inode = 0;
> @@ -315,12 +316,8 @@ static int ocfs2_mknod(struct user_namespace *mnt_userns,
>  	/* get security xattr */
>  	status = ocfs2_init_security_get(inode, dir, &dentry->d_name, &si);
>  	if (status) {
> -		if (status == -EOPNOTSUPP)
> -			si.enable = 0;
> -		else {
> -			mlog_errno(status);
> -			goto leave;
> -		}

Although security_inode_init_security() does not return -EOPNOTSUPP, 
ocfs2_init_security_get() could.  Refer to commit 8154da3d2114 ("ocfs2:
Add incompatible flag for extended attribute").   It was added as a
temporary solution back in 2008, so it is highly unlikely that it is
still needed.

> +		mlog_errno(status);
> +		goto leave;

Without the -EOPNOTSUPP test, ocfs2_mknod() would not create the inode;
and similarly ocfs2_symlink(), below, would not create the symlink.  It
would be safer not to remove the -EOPNOTSUPP test.

>  	}
>  
>  	/* calculate meta data/clusters for setting security and acl xattr */
> @@ -1805,6 +1802,7 @@ static int ocfs2_symlink(struct user_namespace *mnt_userns,
>  	int want_clusters = 0;
>  	int xattr_credits = 0;
>  	struct ocfs2_security_xattr_info si = {
> +		.name = NULL,
>  		.enable = 1,
>  	};
>  	int did_quota = 0, did_quota_inode = 0;
> @@ -1875,12 +1873,8 @@ static int ocfs2_symlink(struct user_namespace *mnt_userns,
>  	/* get security xattr */
>  	status = ocfs2_init_security_get(inode, dir, &dentry->d_name, &si);
>  	if (status) {
> -		if (status == -EOPNOTSUPP)
> -			si.enable = 0;
> -		else {
> -			mlog_errno(status);
> -			goto bail;
> -		}
> +		mlog_errno(status);
> +		goto bail;
>  	}
>  
>  	/* calculate meta data/clusters for setting security xattr */
> diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
> index 95d0611c5fc7..55699c573541 100644
> --- a/fs/ocfs2/xattr.c
> +++ b/fs/ocfs2/xattr.c
> @@ -7259,9 +7259,21 @@ static int ocfs2_xattr_security_set(const struct xattr_handler *handler,
>  static int ocfs2_initxattrs(struct inode *inode, const struct xattr *xattr_array,
>  		     void *fs_info)
>  {
> +	struct ocfs2_security_xattr_info *si = fs_info;
>  	const struct xattr *xattr;
>  	int err = 0;
>  
> +	if (si) {
> +		si->value = kmemdup(xattr_array->value, xattr_array->value_len,
> +				    GFP_KERNEL);
> +		if (!si->value)
> +			return -ENOMEM;
> +
> +		si->name = xattr_array->name;
> +		si->value_len = xattr_array->value_len;
> +		return 0;
> +	}
> +
>  	for (xattr = xattr_array; xattr->name != NULL; xattr++) {
>  		err = ocfs2_xattr_set(inode, OCFS2_XATTR_INDEX_SECURITY,
>  				      xattr->name, xattr->value,
> @@ -7277,13 +7289,23 @@ int ocfs2_init_security_get(struct inode *inode,
>  			    const struct qstr *qstr,
>  			    struct ocfs2_security_xattr_info *si)
>  {
> +	int ret;
> +
>  	/* check whether ocfs2 support feature xattr */
>  	if (!ocfs2_supports_xattr(OCFS2_SB(dir->i_sb)))
>  		return -EOPNOTSUPP;
> -	if (si)
> -		return security_old_inode_init_security(inode, dir, qstr,
> -							&si->name, &si->value,
> -							&si->value_len);
> +	if (si) {
> +		ret = security_inode_init_security(inode, dir, qstr,
> +						   &ocfs2_initxattrs, si);

The "if (unlikely(IS_PRIVATE(inode))"  test exists in both
security_old_inode_init_security() and security_inode_init_security(),
but return different values.  In the former case, it returns
-EOPNOTSUPP.  In the latter case, it returns 0.  The question is
whether or not we need to be concerned about private inodes on ocfs2.  
If private inodes on ocfs2 are possible, then ocsf2_mknod() or
ocfs2_symlink() would fail to create the inode or symlink.

> +		/*
> +		 * security_inode_init_security() does not return -EOPNOTSUPP,
> +		 * we have to check the xattr ourselves.
> +		 */
> +		if (!ret && !si->name)
> +			si->enable = 0;
> +
> +		return ret;
> +	}
>  
>  	return security_inode_init_security(inode, dir, qstr,
>  					    &ocfs2_initxattrs, NULL);

-- 
thanks,

Mimi