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Author SHA1 Message Date
David Howells
cf3cba4a42 vfs: syscall: Add fspick() to select a superblock for reconfiguration 
Provide an fspick() system call that can be used to pick an existing
mountpoint into an fs_context which can thereafter be used to reconfigure a
superblock (equivalent of the superblock side of -o remount).

This looks like:

	int fd = fspick(AT_FDCWD, "/mnt",
			FSPICK_CLOEXEC | FSPICK_NO_AUTOMOUNT);
	fsconfig(fd, FSCONFIG_SET_FLAG, "intr", NULL, 0);
	fsconfig(fd, FSCONFIG_SET_FLAG, "noac", NULL, 0);
	fsconfig(fd, FSCONFIG_CMD_RECONFIGURE, NULL, NULL, 0);

At the point of fspick being called, the file descriptor referring to the
filesystem context is in exactly the same state as the one that was created
by fsopen() after fsmount() has been successfully called.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-api@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
 2019-03-20 18:49:06 -04:00
David Howells
ecdab150fd vfs: syscall: Add fsconfig() for configuring and managing a context 
Add a syscall for configuring a filesystem creation context and triggering
actions upon it, to be used in conjunction with fsopen, fspick and fsmount.

    long fsconfig(int fs_fd, unsigned int cmd, const char *key,
		  const void *value, int aux);

Where fs_fd indicates the context, cmd indicates the action to take, key
indicates the parameter name for parameter-setting actions and, if needed,
value points to a buffer containing the value and aux can give more
information for the value.

The following command IDs are proposed:

 (*) FSCONFIG_SET_FLAG: No value is specified.  The parameter must be
     boolean in nature.  The key may be prefixed with "no" to invert the
     setting. value must be NULL and aux must be 0.

 (*) FSCONFIG_SET_STRING: A string value is specified.  The parameter can
     be expecting boolean, integer, string or take a path.  A conversion to
     an appropriate type will be attempted (which may include looking up as
     a path).  value points to a NUL-terminated string and aux must be 0.

 (*) FSCONFIG_SET_BINARY: A binary blob is specified.  value points to
     the blob and aux indicates its size.  The parameter must be expecting
     a blob.

 (*) FSCONFIG_SET_PATH: A non-empty path is specified.  The parameter must
     be expecting a path object.  value points to a NUL-terminated string
     that is the path and aux is a file descriptor at which to start a
     relative lookup or AT_FDCWD.

 (*) FSCONFIG_SET_PATH_EMPTY: As fsconfig_set_path, but with AT_EMPTY_PATH
     implied.

 (*) FSCONFIG_SET_FD: An open file descriptor is specified.  value must
     be NULL and aux indicates the file descriptor.

 (*) FSCONFIG_CMD_CREATE: Trigger superblock creation.

 (*) FSCONFIG_CMD_RECONFIGURE: Trigger superblock reconfiguration.

For the "set" command IDs, the idea is that the file_system_type will point
to a list of parameters and the types of value that those parameters expect
to take.  The core code can then do the parse and argument conversion and
then give the LSM and FS a cooked option or array of options to use.

Source specification is also done the same way same way, using special keys
"source", "source1", "source2", etc..

[!] Note that, for the moment, the key and value are just glued back
together and handed to the filesystem.  Every filesystem that uses options
uses match_token() and co. to do this, and this will need to be changed -
but not all at once.

Example usage:

    fd = fsopen("ext4", FSOPEN_CLOEXEC);
    fsconfig(fd, fsconfig_set_path, "source", "/dev/sda1", AT_FDCWD);
    fsconfig(fd, fsconfig_set_path_empty, "journal_path", "", journal_fd);
    fsconfig(fd, fsconfig_set_fd, "journal_fd", "", journal_fd);
    fsconfig(fd, fsconfig_set_flag, "user_xattr", NULL, 0);
    fsconfig(fd, fsconfig_set_flag, "noacl", NULL, 0);
    fsconfig(fd, fsconfig_set_string, "sb", "1", 0);
    fsconfig(fd, fsconfig_set_string, "errors", "continue", 0);
    fsconfig(fd, fsconfig_set_string, "data", "journal", 0);
    fsconfig(fd, fsconfig_set_string, "context", "unconfined_u:...", 0);
    fsconfig(fd, fsconfig_cmd_create, NULL, NULL, 0);
    mfd = fsmount(fd, FSMOUNT_CLOEXEC, MS_NOEXEC);

or:

    fd = fsopen("ext4", FSOPEN_CLOEXEC);
    fsconfig(fd, fsconfig_set_string, "source", "/dev/sda1", 0);
    fsconfig(fd, fsconfig_cmd_create, NULL, NULL, 0);
    mfd = fsmount(fd, FSMOUNT_CLOEXEC, MS_NOEXEC);

or:

    fd = fsopen("afs", FSOPEN_CLOEXEC);
    fsconfig(fd, fsconfig_set_string, "source", "#grand.central.org:root.cell", 0);
    fsconfig(fd, fsconfig_cmd_create, NULL, NULL, 0);
    mfd = fsmount(fd, FSMOUNT_CLOEXEC, MS_NOEXEC);

or:

    fd = fsopen("jffs2", FSOPEN_CLOEXEC);
    fsconfig(fd, fsconfig_set_string, "source", "mtd0", 0);
    fsconfig(fd, fsconfig_cmd_create, NULL, NULL, 0);
    mfd = fsmount(fd, FSMOUNT_CLOEXEC, MS_NOEXEC);

Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-api@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
 2019-03-20 18:49:06 -04:00
David Howells
007ec26cdc vfs: Implement logging through fs_context 
Implement the ability for filesystems to log error, warning and
informational messages through the fs_context.  These can be extracted by
userspace by reading from an fd created by fsopen().

Error messages are prefixed with "e ", warnings with "w " and informational
messages with "i ".

Inside the kernel, formatted messages are malloc'd but unformatted messages
are not copied if they're either in the core .rodata section or in the
.rodata section of the filesystem module pinned by fs_context::fs_type.
The messages are only good till the fs_type is released.

Note that the logging object is shared between duplicated fs_context
structures.  This is so that such as NFS which do a mount within a mount
can get at least some of the errors from the inner mount.

Five logging functions are provided for this:

 (1) void logfc(struct fs_context *fc, const char *fmt, ...);

     This logs a message into the context.  If the buffer is full, the
     earliest message is discarded.

 (2) void errorf(fc, fmt, ...);

     This wraps logfc() to log an error.

 (3) void invalf(fc, fmt, ...);

     This wraps errorf() and returns -EINVAL for convenience.

 (4) void warnf(fc, fmt, ...);

     This wraps logfc() to log a warning.

 (5) void infof(fc, fmt, ...);

     This wraps logfc() to log an informational message.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
 2019-03-20 18:49:06 -04:00
David Howells
24dcb3d90a 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>
 2019-03-20 18:49:06 -04:00