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

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Date:   Tue, 29 May 2018 14:55:25 +0200
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Miklos Szeredi <miklos@...redi.hu>,
        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>
Subject: Re: [PATCH] fuse: Ensure posix acls are translated outside of init_user_ns

On Tue, May 29, 2018 at 2:42 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> 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.


No, sorry.  I'll queue this up for 4.18.

Just wanted to finish off overlayfs stuff before getting into fuse.

Thanks,
Miklos

>
>>
>>> 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
>>> +};