linux-kernel - Re: [PATCH] fuse: Ensure posix acls are translated outside of init_user

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Message-ID: <877enmskec.fsf@xmission.com>
Date:   Tue, 29 May 2018 07:42:35 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Alban Crequy <alban@...volk.io>,
        Seth Forshee <seth.forshee@...onical.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Dongsu Park <dongsu@...volk.io>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Miklos Szeredi <mszeredi@...hat.com>
Subject: Re: [PATCH] fuse: Ensure posix acls are translated outside of init_user_ns

ebiederm@...ssion.com (Eric W. Biederman) writes:

> ebiederm@...ssion.com (Eric W. Biederman) writes:
>
>> Ensure the translation happens by failing to read or write
>> posix acls when the filesystem has not indicated it supports
>> posix acls.
>>
>> This ensures that modern cached posix acl support is available
>> and used when dealing with posix acls.  This is important
>> because only that path has the code to convernt the uids and
>> gids in posix acls into the user namespace of a fuse filesystem.
>>
>> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
>> ---
>
> ping.
>
> Miklos are you around where you can look at this?

Perhaps I got the wrong email address.

Ping?


>
>> Miklos after several attempts to handle this better last cycle.  I
>> figure we should go with the stupid version for now.  I think I know
>> how to do better but I don't want that to gate forward progress on
>> fully unprivileged fuse mounts.  Especially as this is the last known
>> issue to deal with.
>>
>>  fs/fuse/fuse_i.h |  1 +
>>  fs/fuse/inode.c  |  7 +++++++
>>  fs/fuse/xattr.c  | 43 +++++++++++++++++++++++++++++++++++++++++++
>>  3 files changed, 51 insertions(+)
>>
>> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
>> index f630951df8dc..5256ad333b05 100644
>> --- a/fs/fuse/fuse_i.h
>> +++ b/fs/fuse/fuse_i.h
>> @@ -985,6 +985,7 @@ ssize_t fuse_listxattr(struct dentry *entry, char *list, size_t size);
>>  int fuse_removexattr(struct inode *inode, const char *name);
>>  extern const struct xattr_handler *fuse_xattr_handlers[];
>>  extern const struct xattr_handler *fuse_acl_xattr_handlers[];
>> +extern const struct xattr_handler *fuse_no_acl_xattr_handlers[];
>>  
>>  struct posix_acl;
>>  struct posix_acl *fuse_get_acl(struct inode *inode, int type);
>> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
>> index 1643043d4fe5..22c76cf8c2e3 100644
>> --- a/fs/fuse/inode.c
>> +++ b/fs/fuse/inode.c
>> @@ -1100,6 +1100,13 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
>>  	    file->f_cred->user_ns != sb->s_user_ns)
>>  		goto err_fput;
>>  
>> +	/*
>> +	 * If we are not in the initial user namespace posix
>> +	 * acls must be translated.
>> +	 */
>> +	if (sb->s_user_ns != &init_user_ns)
>> +		sb->s_xattr = fuse_no_acl_xattr_handlers;
>> +
>>  	fc = kmalloc(sizeof(*fc), GFP_KERNEL);
>>  	err = -ENOMEM;
>>  	if (!fc)
>> diff --git a/fs/fuse/xattr.c b/fs/fuse/xattr.c
>> index 3caac46b08b0..433717640f78 100644
>> --- a/fs/fuse/xattr.c
>> +++ b/fs/fuse/xattr.c
>> @@ -192,6 +192,26 @@ static int fuse_xattr_set(const struct xattr_handler *handler,
>>  	return fuse_setxattr(inode, name, value, size, flags);
>>  }
>>  
>> +static bool no_xattr_list(struct dentry *dentry)
>> +{
>> +	return false;
>> +}
>> +
>> +static int no_xattr_get(const struct xattr_handler *handler,
>> +			struct dentry *dentry, struct inode *inode,
>> +			const char *name, void *value, size_t size)
>> +{
>> +	return -EOPNOTSUPP;
>> +}
>> +
>> +static int no_xattr_set(const struct xattr_handler *handler,
>> +			struct dentry *dentry, struct inode *nodee,
>> +			const char *name, const void *value,
>> +			size_t size, int flags)
>> +{
>> +	return -EOPNOTSUPP;
>> +}
>> +
>>  static const struct xattr_handler fuse_xattr_handler = {
>>  	.prefix = "",
>>  	.get    = fuse_xattr_get,
>> @@ -209,3 +229,26 @@ const struct xattr_handler *fuse_acl_xattr_handlers[] = {
>>  	&fuse_xattr_handler,
>>  	NULL
>>  };
>> +
>> +static const struct xattr_handler fuse_no_acl_access_xattr_handler = {
>> +	.name  = XATTR_NAME_POSIX_ACL_ACCESS,
>> +	.flags = ACL_TYPE_ACCESS,
>> +	.list  = no_xattr_list,
>> +	.get   = no_xattr_get,
>> +	.set   = no_xattr_set,
>> +};
>> +
>> +static const struct xattr_handler fuse_no_acl_default_xattr_handler = {
>> +	.name  = XATTR_NAME_POSIX_ACL_DEFAULT,
>> +	.flags = ACL_TYPE_ACCESS,
>> +	.list  = no_xattr_list,
>> +	.get   = no_xattr_get,
>> +	.set   = no_xattr_set,
>> +};
>> +
>> +const struct xattr_handler *fuse_no_acl_xattr_handlers[] = {
>> +	&fuse_no_acl_access_xattr_handler,
>> +	&fuse_no_acl_default_xattr_handler,
>> +	&fuse_xattr_handler,
>> +	NULL
>> +};