From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: [PATCH 30/34] vfs: syscall: Add fsmount() to create a mount for a superblock [ver #12] From: David Howells To: viro@zeniv.linux.org.uk Cc: linux-api@vger.kernel.org, torvalds@linux-foundation.org, dhowells@redhat.com, ebiederm@xmission.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, mszeredi@redhat.com Date: Fri, 21 Sep 2018 17:34:12 +0100 Message-ID: <153754765237.17872.17624067695858838756.stgit@warthog.procyon.org.uk> In-Reply-To: <153754740781.17872.7869536526927736855.stgit@warthog.procyon.org.uk> References: <153754740781.17872.7869536526927736855.stgit@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: Provide a system call by which a filesystem opened with fsopen() and configured by a series of fsconfig() calls can have a detached mount object created for it. This mount object can then be attached to the VFS mount hierarchy using move_mount() by passing the returned file descriptor as the from directory fd. The system call looks like: int mfd = fsmount(int fsfd, unsigned int flags, unsigned int ms_flags); where fsfd is the file descriptor returned by fsopen(). flags can be 0 or FSMOUNT_CLOEXEC. ms_flags is a bitwise-OR of the following flags: MS_RDONLY MS_NOSUID MS_NODEV MS_NOEXEC MS_NOATIME MS_NODIRATIME MS_RELATIME MS_STRICTATIME MS_UNBINDABLE MS_PRIVATE MS_SLAVE MS_SHARED In the event that fsmount() fails, it may be possible to get an error message by calling read() on fsfd. If no message is available, ENODATA will be reported. Signed-off-by: David Howells cc: linux-api@vger.kernel.org --- arch/x86/entry/syscalls/syscall_32.tbl | 1 arch/x86/entry/syscalls/syscall_64.tbl | 1 fs/namespace.c | 125 +++++++++++++++++++++++++++++++- include/linux/syscalls.h | 1 include/uapi/linux/fs.h | 2 + 5 files changed, 126 insertions(+), 4 deletions(-) diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl index f9970310c126..c78b68256f8a 100644 --- a/arch/x86/entry/syscalls/syscall_32.tbl +++ b/arch/x86/entry/syscalls/syscall_32.tbl @@ -402,3 +402,4 @@ 388 i386 move_mount sys_move_mount __ia32_sys_move_mount 389 i386 fsopen sys_fsopen __ia32_sys_fsopen 390 i386 fsconfig sys_fsconfig __ia32_sys_fsconfig +391 i386 fsmount sys_fsmount __ia32_sys_fsmount diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl index 4185d36e03bb..d44ead5d4368 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -347,6 +347,7 @@ 336 common move_mount __x64_sys_move_mount 337 common fsopen __x64_sys_fsopen 338 common fsconfig __x64_sys_fsconfig +339 common fsmount __x64_sys_fsmount # # x32-specific system call numbers start at 512 to avoid cache impact diff --git a/fs/namespace.c b/fs/namespace.c index 156261d03c12..4dfe7e23b7ee 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2463,7 +2463,7 @@ static int do_move_mount(struct path *old_path, struct path *new_path) attached = mnt_has_parent(old); /* - * We need to allow open_tree(OPEN_TREE_CLONE) followed by + * We need to allow open_tree(OPEN_TREE_CLONE) or fsmount() followed by * move_mount(), but mustn't allow "/" to be moved. */ if (old->mnt_ns && !attached) @@ -3329,9 +3329,126 @@ struct vfsmount *kern_mount(struct file_system_type *type) EXPORT_SYMBOL_GPL(kern_mount); /* - * Move a mount from one place to another. - * In combination with open_tree(OPEN_TREE_CLONE [| AT_RECURSIVE]) it can be - * used to copy a mount subtree. + * Create a kernel mount representation for a new, prepared superblock + * (specified by fs_fd) and attach to an open_tree-like file descriptor. + */ +SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags, unsigned int, ms_flags) +{ + struct fs_context *fc; + struct file *file; + struct path newmount; + struct fd f; + unsigned int mnt_flags = 0; + long ret; + + if (!may_mount()) + return -EPERM; + + if ((flags & ~(FSMOUNT_CLOEXEC)) != 0) + return -EINVAL; + + if (ms_flags & ~(MS_RDONLY | MS_NOSUID | MS_NODEV | MS_NOEXEC | + MS_NOATIME | MS_NODIRATIME | MS_RELATIME | + MS_STRICTATIME)) + return -EINVAL; + + if (ms_flags & MS_RDONLY) + mnt_flags |= MNT_READONLY; + if (ms_flags & MS_NOSUID) + mnt_flags |= MNT_NOSUID; + if (ms_flags & MS_NODEV) + mnt_flags |= MNT_NODEV; + if (ms_flags & MS_NOEXEC) + mnt_flags |= MNT_NOEXEC; + if (ms_flags & MS_NODIRATIME) + mnt_flags |= MNT_NODIRATIME; + + if (ms_flags & MS_STRICTATIME) { + if (ms_flags & MS_NOATIME) + return -EINVAL; + } else if (ms_flags & MS_NOATIME) { + mnt_flags |= MNT_NOATIME; + } else { + mnt_flags |= MNT_RELATIME; + } + + f = fdget(fs_fd); + if (!f.file) + return -EBADF; + + ret = -EINVAL; + if (f.file->f_op != &fscontext_fops) + goto err_fsfd; + + fc = f.file->private_data; + + /* There must be a valid superblock or we can't mount it */ + ret = -EINVAL; + if (!fc->root) + goto err_fsfd; + + ret = -EPERM; + if (mount_too_revealing(fc->root->d_sb, &mnt_flags)) { + pr_warn("VFS: Mount too revealing\n"); + goto err_fsfd; + } + + ret = mutex_lock_interruptible(&fc->uapi_mutex); + if (ret < 0) + goto err_fsfd; + + ret = -EBUSY; + if (fc->phase != FS_CONTEXT_AWAITING_MOUNT) + goto err_unlock; + + ret = -EPERM; + if ((fc->sb_flags & SB_MANDLOCK) && !may_mandlock()) + goto err_unlock; + + newmount.mnt = vfs_create_mount(fc, mnt_flags); + if (IS_ERR(newmount.mnt)) { + ret = PTR_ERR(newmount.mnt); + goto err_unlock; + } + newmount.dentry = dget(fc->root); + + /* We've done the mount bit - now move the file context into more or + * less the same state as if we'd done an fspick(). We don't want to + * do any memory allocation or anything like that at this point as we + * don't want to have to handle any errors incurred. + */ + vfs_clean_context(fc); + + /* Attach to an apparent O_PATH fd with a note that we need to unmount + * it, not just simply put it. + */ + file = dentry_open(&newmount, O_PATH, fc->cred); + if (IS_ERR(file)) { + ret = PTR_ERR(file); + goto err_path; + } + file->f_mode |= FMODE_NEED_UNMOUNT; + + ret = get_unused_fd_flags((flags & FSMOUNT_CLOEXEC) ? O_CLOEXEC : 0); + if (ret >= 0) + fd_install(ret, file); + else + fput(file); + +err_path: + path_put(&newmount); +err_unlock: + mutex_unlock(&fc->uapi_mutex); +err_fsfd: + fdput(f); + return ret; +} + +/* + * Move a mount from one place to another. In combination with + * fsopen()/fsmount() this is used to install a new mount and in combination + * with open_tree(OPEN_TREE_CLONE [| AT_RECURSIVE]) it can be used to copy + * a mount subtree. * * Note the flags value is a combination of MOVE_MOUNT_* flags. */ diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 4ab15fdf8aea..4697fad47789 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -913,6 +913,7 @@ asmlinkage long sys_move_mount(int from_dfd, const char __user *from_path, asmlinkage long sys_fsopen(const char __user *fs_name, unsigned int flags); asmlinkage long sys_fsconfig(int fs_fd, unsigned int cmd, const char __user *key, const void __user *value, int aux); +asmlinkage long sys_fsmount(int fs_fd, unsigned int flags, unsigned int ms_flags); /* * Architecture-specific system calls diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index fecbae30a30d..10281d582e28 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h @@ -349,6 +349,8 @@ typedef int __bitwise __kernel_rwf_t; */ #define FSOPEN_CLOEXEC 0x00000001 +#define FSMOUNT_CLOEXEC 0x00000001 + /* * The type of fsconfig() call made. */