From: Jann Horn <jannh@google.com>
To: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
Linux API <linux-api@vger.kernel.org>,
linux-fsdevel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
linux-security-module <linux-security-module@vger.kernel.org>
Subject: Re: [PATCH 02/10] vfs: syscall: Add move_mount(2) to move mounts around
Date: Wed, 20 Feb 2019 17:23:46 +0100 [thread overview]
Message-ID: <CAG48ez0fvv4CT5S7xgW92Ouad8N-r9RY89QbUwRVYd9DLKePiw@mail.gmail.com> (raw)
In-Reply-To: <155059611887.17079.12991580316407924257.stgit@warthog.procyon.org.uk>
On Tue, Feb 19, 2019 at 6:08 PM David Howells <dhowells@redhat.com> wrote:
> Add a move_mount() system call that will move a mount from one place to
> another and, in the next commit, allow to attach an unattached mount tree.
>
> The new system call looks like the following:
>
> int move_mount(int from_dfd, const char *from_path,
> int to_dfd, const char *to_path,
> unsigned int flags);
>
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: linux-api@vger.kernel.org
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> ---
[...]
> +/*
> + * Move a mount from one place to another.
> + *
> + * Note the flags value is a combination of MOVE_MOUNT_* flags.
> + */
> +SYSCALL_DEFINE5(move_mount,
> + int, from_dfd, const char *, from_pathname,
> + int, to_dfd, const char *, to_pathname,
> + unsigned int, flags)
> +{
> + struct path from_path, to_path;
> + unsigned int lflags;
> + int ret = 0;
> +
> + if (!may_mount())
> + return -EPERM;
> +
> + if (flags & ~MOVE_MOUNT__MASK)
> + return -EINVAL;
> +
> + /* If someone gives a pathname, they aren't permitted to move
> + * from an fd that requires unmount as we can't get at the flag
> + * to clear it afterwards.
> + */
> + lflags = 0;
> + if (flags & MOVE_MOUNT_F_SYMLINKS) lflags |= LOOKUP_FOLLOW;
> + if (flags & MOVE_MOUNT_F_AUTOMOUNTS) lflags |= LOOKUP_AUTOMOUNT;
> + if (flags & MOVE_MOUNT_F_EMPTY_PATH) lflags |= LOOKUP_EMPTY;
> +
> + ret = user_path_at(from_dfd, from_pathname, lflags, &from_path);
> + if (ret < 0)
> + return ret;
> +
> + lflags = 0;
> + if (flags & MOVE_MOUNT_T_SYMLINKS) lflags |= LOOKUP_FOLLOW;
> + if (flags & MOVE_MOUNT_T_AUTOMOUNTS) lflags |= LOOKUP_AUTOMOUNT;
> + if (flags & MOVE_MOUNT_T_EMPTY_PATH) lflags |= LOOKUP_EMPTY;
> +
> + ret = user_path_at(to_dfd, to_pathname, lflags, &to_path);
> + if (ret < 0)
> + goto out_from;
> +
> + ret = security_move_mount(&from_path, &to_path);
> + if (ret < 0)
> + goto out_to;
Wouldn't you want to call this from do_move_mount() instead for
consistency? If MS_MOVE and this thing perform the same logical
operation, they should probably also call the same LSM hook.
> + ret = do_move_mount(&from_path, &to_path);
> +
> +out_to:
> + path_put(&to_path);
> +out_from:
> + path_put(&from_path);
> + return ret;
> +}
[...]
> diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
> index fd7ae2e7eccf..3634e065836c 100644
> --- a/include/uapi/linux/mount.h
> +++ b/include/uapi/linux/mount.h
> @@ -61,4 +61,15 @@
> #define OPEN_TREE_CLONE 1 /* Clone the target tree and attach the clone */
> #define OPEN_TREE_CLOEXEC O_CLOEXEC /* Close the file on execve() */
>
> +/*
> + * move_mount() flags.
> + */
> +#define MOVE_MOUNT_F_SYMLINKS 0x00000001 /* Follow symlinks on from path */
"Follow symlinks" sounds a bit misleading. LOOKUP_NOFOLLOW only
applies to the last element of the path; and there is a pending
patchset that's going to let userspace ask the kernel to actually not
follow *any* symlinks on the path with O_NOSYMLINKS, so this might
confuse people. Maybe change the comment to "don't follow trailing
symlink", or something like that?
next prev parent reply other threads:[~2019-02-20 16:24 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-19 17:08 [PATCH 00/10] VFS: Provide new mount UAPI David Howells
2019-02-19 17:08 ` [PATCH 01/10] vfs: syscall: Add open_tree(2) to reference or clone a mount David Howells
2019-02-19 17:08 ` [PATCH 02/10] vfs: syscall: Add move_mount(2) to move mounts around David Howells
2019-02-20 12:32 ` Alan Jenkins
2019-02-20 12:41 ` Alan Jenkins
2019-02-20 16:23 ` Jann Horn [this message]
2019-07-08 12:02 ` Tetsuo Handa
2019-07-08 13:18 ` Al Viro
2019-07-08 17:12 ` Eric W. Biederman
2019-07-08 18:01 ` Al Viro
2019-07-08 18:13 ` Al Viro
2019-07-08 20:21 ` Al Viro
2019-07-09 0:13 ` Eric W. Biederman
2019-07-09 10:51 ` Tetsuo Handa
2019-07-22 10:12 ` Tetsuo Handa
2019-07-23 4:16 ` John Johansen
2019-07-23 13:45 ` Tetsuo Handa
2019-08-06 10:43 ` Tetsuo Handa
2019-08-22 3:51 ` [RFC][PATCH] fix d_absolute_path() interplay with fsmount() Al Viro
2019-08-30 10:11 ` Tetsuo Handa
2019-07-23 21:45 ` [PATCH 02/10] vfs: syscall: Add move_mount(2) to move mounts around James Morris
2019-07-23 23:30 ` Al Viro
2019-02-19 17:08 ` [PATCH 03/10] teach move_mount(2) to work with OPEN_TREE_CLONE David Howells
2019-02-20 18:59 ` Alan Jenkins
2019-02-26 17:45 ` Alan Jenkins
2019-02-19 17:08 ` [PATCH 04/10] Make anon_inodes unconditional David Howells
2019-02-19 17:09 ` [PATCH 05/10] vfs: syscall: Add fsopen() to prepare for superblock creation David Howells
2019-02-19 17:09 ` [PATCH 06/10] vfs: Implement logging through fs_context David Howells
2019-02-19 17:09 ` [PATCH 07/10] vfs: syscall: Add fsconfig() for configuring and managing a context David Howells
2019-02-19 17:09 ` [PATCH 08/10] vfs: syscall: Add fsmount() to create a mount for a superblock David Howells
2019-02-19 17:09 ` [PATCH 09/10] vfs: syscall: Add fspick() to select a superblock for reconfiguration David Howells
2019-02-19 17:09 ` [PATCH 10/10] vfs: Add a sample program for the new mount API David Howells
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