vfs: syscall: Add fsopen() to prepare for superblock creation
Provide an fsopen() system call that starts the process of preparing to
create a superblock that will then be mountable, using an fd as a context
handle. fsopen() is given the name of the filesystem that will be used:
int mfd = fsopen(const char *fsname, unsigned int flags);
where flags can be 0 or FSOPEN_CLOEXEC.
For example:
sfd = fsopen("ext4", FSOPEN_CLOEXEC);
fsconfig(sfd, FSCONFIG_SET_PATH, "source", "/dev/sda1", AT_FDCWD);
fsconfig(sfd, FSCONFIG_SET_FLAG, "noatime", NULL, 0);
fsconfig(sfd, FSCONFIG_SET_FLAG, "acl", NULL, 0);
fsconfig(sfd, FSCONFIG_SET_FLAG, "user_xattr", NULL, 0);
fsconfig(sfd, FSCONFIG_SET_STRING, "sb", "1", 0);
fsconfig(sfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
fsinfo(sfd, NULL, ...); // query new superblock attributes
mfd = fsmount(sfd, FSMOUNT_CLOEXEC, MS_RELATIME);
move_mount(mfd, "", sfd, AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
sfd = fsopen("afs", -1);
fsconfig(fd, FSCONFIG_SET_STRING, "source",
"#grand.central.org:root.cell", 0);
fsconfig(fd, FSCONFIG_CMD_CREATE, NULL, NULL, 0);
mfd = fsmount(sfd, 0, MS_NODEV);
move_mount(mfd, "", sfd, AT_FDCWD, "/mnt", MOVE_MOUNT_F_EMPTY_PATH);
If an error is reported at any step, an error message may be available to be
read() back (ENODATA will be reported if there isn't an error available) in
the form:
"e <subsys>:<problem>"
"e SELinux:Mount on mountpoint not permitted"
Once fsmount() has been called, further fsconfig() calls will incur EBUSY,
even if the fsmount() fails. read() is still possible to retrieve error
information.
The fsopen() syscall creates a mount context and hangs it of the fd that it
returns.
Netlink is not used because it is optional and would make the core VFS
dependent on the networking layer and also potentially add network
namespace issues.
Note that, for the moment, the caller must have SYS_CAP_ADMIN to use
fsopen().
Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-api@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 0db9eff..37fd1fc 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -400,7 +400,8 @@
386 i386 rseq sys_rseq __ia32_sys_rseq
387 i386 open_tree sys_open_tree __ia32_sys_open_tree
388 i386 move_mount sys_move_mount __ia32_sys_move_mount
-# don't use numbers 389 through 392, add new calls at the end
+389 i386 fsopen sys_fsopen __ia32_sys_fsopen
+# don't use numbers 390 through 392, add new calls at the end
393 i386 semget sys_semget __ia32_sys_semget
394 i386 semctl sys_semctl __ia32_compat_sys_semctl
395 i386 shmget sys_shmget __ia32_sys_shmget
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 0440f0e..511608a 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -345,6 +345,7 @@
334 common rseq __x64_sys_rseq
335 common open_tree __x64_sys_open_tree
336 common move_mount __x64_sys_move_mount
+337 common fsopen __x64_sys_fsopen
# don't use numbers 387 through 423, add new calls after the last
# 'common' entry
424 common pidfd_send_signal __x64_sys_pidfd_send_signal
diff --git a/fs/Makefile b/fs/Makefile
index 35945f8..5a51bc2 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -13,7 +13,7 @@
seq_file.o xattr.o libfs.o fs-writeback.o \
pnode.o splice.o sync.o utimes.o d_path.o \
stack.o fs_struct.o statfs.o fs_pin.o nsfs.o \
- fs_types.o fs_context.o fs_parser.o
+ fs_types.o fs_context.o fs_parser.o fsopen.o
ifeq ($(CONFIG_BLOCK),y)
obj-y += buffer.o block_dev.o direct-io.o mpage.o
diff --git a/fs/fs_context.c b/fs/fs_context.c
index 87e3546..eb806fa 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -271,6 +271,8 @@
fc->cred = get_current_cred();
fc->net_ns = get_net(current->nsproxy->net_ns);
+ mutex_init(&fc->uapi_mutex);
+
switch (purpose) {
case FS_CONTEXT_FOR_MOUNT:
fc->user_ns = get_user_ns(fc->cred->user_ns);
@@ -353,6 +355,8 @@
if (!fc)
return ERR_PTR(-ENOMEM);
+ mutex_init(&fc->uapi_mutex);
+
fc->fs_private = NULL;
fc->s_fs_info = NULL;
fc->source = NULL;
diff --git a/fs/fsopen.c b/fs/fsopen.c
new file mode 100644
index 0000000..d256f1a
--- /dev/null
+++ b/fs/fsopen.c
@@ -0,0 +1,88 @@
+/* Filesystem access-by-fd.
+ *
+ * Copyright (C) 2017 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/fs_context.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/syscalls.h>
+#include <linux/security.h>
+#include <linux/anon_inodes.h>
+#include <linux/namei.h>
+#include <linux/file.h>
+#include <uapi/linux/mount.h>
+#include "mount.h"
+
+static int fscontext_release(struct inode *inode, struct file *file)
+{
+ struct fs_context *fc = file->private_data;
+
+ if (fc) {
+ file->private_data = NULL;
+ put_fs_context(fc);
+ }
+ return 0;
+}
+
+const struct file_operations fscontext_fops = {
+ .release = fscontext_release,
+ .llseek = no_llseek,
+};
+
+/*
+ * Attach a filesystem context to a file and an fd.
+ */
+static int fscontext_create_fd(struct fs_context *fc, unsigned int o_flags)
+{
+ int fd;
+
+ fd = anon_inode_getfd("fscontext", &fscontext_fops, fc,
+ O_RDWR | o_flags);
+ if (fd < 0)
+ put_fs_context(fc);
+ return fd;
+}
+
+/*
+ * Open a filesystem by name so that it can be configured for mounting.
+ *
+ * We are allowed to specify a container in which the filesystem will be
+ * opened, thereby indicating which namespaces will be used (notably, which
+ * network namespace will be used for network filesystems).
+ */
+SYSCALL_DEFINE2(fsopen, const char __user *, _fs_name, unsigned int, flags)
+{
+ struct file_system_type *fs_type;
+ struct fs_context *fc;
+ const char *fs_name;
+
+ if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))
+ return -EPERM;
+
+ if (flags & ~FSOPEN_CLOEXEC)
+ return -EINVAL;
+
+ fs_name = strndup_user(_fs_name, PAGE_SIZE);
+ if (IS_ERR(fs_name))
+ return PTR_ERR(fs_name);
+
+ fs_type = get_fs_type(fs_name);
+ kfree(fs_name);
+ if (!fs_type)
+ return -ENODEV;
+
+ fc = fs_context_for_mount(fs_type, 0);
+ put_filesystem(fs_type);
+ if (IS_ERR(fc))
+ return PTR_ERR(fc);
+
+ fc->phase = FS_CONTEXT_CREATE_PARAMS;
+ return fscontext_create_fd(fc, flags & FSOPEN_CLOEXEC ? O_CLOEXEC : 0);
+}
diff --git a/include/linux/fs_context.h b/include/linux/fs_context.h
index eaca452..7ab8b44 100644
--- a/include/linux/fs_context.h
+++ b/include/linux/fs_context.h
@@ -15,6 +15,7 @@
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/security.h>
+#include <linux/mutex.h>
struct cred;
struct dentry;
@@ -35,6 +36,19 @@
};
/*
+ * Userspace usage phase for fsopen/fspick.
+ */
+enum fs_context_phase {
+ FS_CONTEXT_CREATE_PARAMS, /* Loading params for sb creation */
+ FS_CONTEXT_CREATING, /* A superblock is being created */
+ FS_CONTEXT_AWAITING_MOUNT, /* Superblock created, awaiting fsmount() */
+ FS_CONTEXT_AWAITING_RECONF, /* Awaiting initialisation for reconfiguration */
+ FS_CONTEXT_RECONF_PARAMS, /* Loading params for reconfiguration */
+ FS_CONTEXT_RECONFIGURING, /* Reconfiguring the superblock */
+ FS_CONTEXT_FAILED, /* Failed to correctly transition a context */
+};
+
+/*
* Type of parameter value.
*/
enum fs_value_type {
@@ -74,6 +88,7 @@
*/
struct fs_context {
const struct fs_context_operations *ops;
+ struct mutex uapi_mutex; /* Userspace access mutex */
struct file_system_type *fs_type;
void *fs_private; /* The filesystem's context */
struct dentry *root; /* The root and superblock */
@@ -88,6 +103,7 @@
unsigned int sb_flags_mask; /* Superblock flags that were changed */
unsigned int lsm_flags; /* Information flags from the fs to the LSM */
enum fs_context_purpose purpose:8;
+ enum fs_context_phase phase:8; /* The phase the context is in */
bool need_free:1; /* Need to call ops->free() */
bool global:1; /* Goes into &init_user_ns */
};
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 84347fc..0c9bd54 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -989,6 +989,7 @@
asmlinkage long sys_move_mount(int from_dfd, const char __user *from_path,
int to_dfd, const char __user *to_path,
unsigned int ms_flags);
+asmlinkage long sys_fsopen(const char __user *fs_name, unsigned int flags);
asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
siginfo_t __user *info,
unsigned int flags);
diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
index 3634e06..7570df4 100644
--- a/include/uapi/linux/mount.h
+++ b/include/uapi/linux/mount.h
@@ -72,4 +72,9 @@
#define MOVE_MOUNT_T_EMPTY_PATH 0x00000040 /* Empty to path permitted */
#define MOVE_MOUNT__MASK 0x00000077
+/*
+ * fsopen() flags.
+ */
+#define FSOPEN_CLOEXEC 0x00000001
+
#endif /* _UAPI_LINUX_MOUNT_H */
