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8cb08329b0
In order to support mounts from namespaces other than init_user_ns, fuse must translate uids and gids to/from the userns of the process servicing requests on /dev/fuse. This patch does that, with a couple of restrictions on the namespace: - The userns for the fuse connection is fixed to the namespace from which /dev/fuse is opened. - The namespace must be the same as s_user_ns. These restrictions simplify the implementation by avoiding the need to pass around userns references and by allowing fuse to rely on the checks in setattr_prepare for ownership changes. Either restriction could be relaxed in the future if needed. For cuse the userns used is the opener of /dev/cuse. Semantically the cuse support does not appear safe for unprivileged users. Practically the permissions on /dev/cuse only make it accessible to the global root user. If something slips through the cracks in a user namespace the only users who will be able to use the cuse device are those users mapped into the user namespace. Translation in the posix acl is updated to use the uuser namespace of the filesystem. Avoiding cases which might bypass this translation is handled in a following change. This change is stronlgy based on a similar change from Seth Forshee and Dongsu Park. Cc: Seth Forshee <seth.forshee@canonical.com> Cc: Dongsu Park <dongsu@kinvolk.io> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
100 lines
2.2 KiB
C
100 lines
2.2 KiB
C
/*
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* FUSE: Filesystem in Userspace
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* Copyright (C) 2016 Canonical Ltd. <seth.forshee@canonical.com>
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*
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* This program can be distributed under the terms of the GNU GPL.
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* See the file COPYING.
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*/
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#include "fuse_i.h"
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#include <linux/posix_acl.h>
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#include <linux/posix_acl_xattr.h>
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struct posix_acl *fuse_get_acl(struct inode *inode, int type)
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{
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struct fuse_conn *fc = get_fuse_conn(inode);
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int size;
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const char *name;
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void *value = NULL;
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struct posix_acl *acl;
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if (!fc->posix_acl || fc->no_getxattr)
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return NULL;
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if (type == ACL_TYPE_ACCESS)
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name = XATTR_NAME_POSIX_ACL_ACCESS;
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else if (type == ACL_TYPE_DEFAULT)
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name = XATTR_NAME_POSIX_ACL_DEFAULT;
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else
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return ERR_PTR(-EOPNOTSUPP);
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value = kmalloc(PAGE_SIZE, GFP_KERNEL);
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if (!value)
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return ERR_PTR(-ENOMEM);
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size = fuse_getxattr(inode, name, value, PAGE_SIZE);
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if (size > 0)
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acl = posix_acl_from_xattr(fc->user_ns, value, size);
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else if ((size == 0) || (size == -ENODATA) ||
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(size == -EOPNOTSUPP && fc->no_getxattr))
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acl = NULL;
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else if (size == -ERANGE)
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acl = ERR_PTR(-E2BIG);
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else
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acl = ERR_PTR(size);
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kfree(value);
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return acl;
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}
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int fuse_set_acl(struct inode *inode, struct posix_acl *acl, int type)
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{
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struct fuse_conn *fc = get_fuse_conn(inode);
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const char *name;
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int ret;
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if (!fc->posix_acl || fc->no_setxattr)
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return -EOPNOTSUPP;
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if (type == ACL_TYPE_ACCESS)
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name = XATTR_NAME_POSIX_ACL_ACCESS;
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else if (type == ACL_TYPE_DEFAULT)
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name = XATTR_NAME_POSIX_ACL_DEFAULT;
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else
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return -EINVAL;
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if (acl) {
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/*
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* Fuse userspace is responsible for updating access
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* permissions in the inode, if needed. fuse_setxattr
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* invalidates the inode attributes, which will force
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* them to be refreshed the next time they are used,
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* and it also updates i_ctime.
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*/
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size_t size = posix_acl_xattr_size(acl->a_count);
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void *value;
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if (size > PAGE_SIZE)
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return -E2BIG;
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value = kmalloc(size, GFP_KERNEL);
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if (!value)
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return -ENOMEM;
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ret = posix_acl_to_xattr(fc->user_ns, acl, value, size);
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if (ret < 0) {
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kfree(value);
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return ret;
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}
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ret = fuse_setxattr(inode, name, value, size, 0);
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kfree(value);
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} else {
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ret = fuse_removexattr(inode, name);
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}
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forget_all_cached_acls(inode);
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fuse_invalidate_attr(inode);
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return ret;
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}
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