From patchwork Sun Jun 3 00:55:37 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Al Viro X-Patchwork-Id: 10445047 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id ABF1B6028E for ; Sun, 3 Jun 2018 00:56:17 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 96BE928A4B for ; Sun, 3 Jun 2018 00:56:17 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 8934728A89; Sun, 3 Jun 2018 00:56:17 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00, MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C1D9628A4B for ; Sun, 3 Jun 2018 00:56:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750987AbeFCA4C (ORCPT ); Sat, 2 Jun 2018 20:56:02 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:52478 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750871AbeFCA4B (ORCPT ); Sat, 2 Jun 2018 20:56:01 -0400 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.87 #1 (Red Hat Linux)) id 1fPHJ3-0003Dw-Cg; Sun, 03 Jun 2018 00:55:43 +0000 Date: Sun, 3 Jun 2018 01:55:37 +0100 From: Al Viro To: David Howells Cc: Christoph Hellwig , linux-fsdevel@vger.kernel.org, linux-afs@lists.infradead.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org Subject: [PATCH][RFC] open_tree(2) (was Re: [PATCH 30/32] vfs: Allow cloning of a mount tree with open(O_PATH|O_CLONE_MOUNT) [ver #8]) Message-ID: <20180603005532.GZ30522@ZenIV.linux.org.uk> References: <20180602040434.GW30522@ZenIV.linux.org.uk> <20180601063928.GS30522@ZenIV.linux.org.uk> <152720672288.9073.9868393448836301272.stgit@warthog.procyon.org.uk> <152720691829.9073.10564431140980997005.stgit@warthog.procyon.org.uk> <20180601062654.GA32397@infradead.org> <7067.1527841663@warthog.procyon.org.uk> <20180602030913.GU30522@ZenIV.linux.org.uk> <20180602034255.GV30522@ZenIV.linux.org.uk> <21804.1527954321@warthog.procyon.org.uk> <20180602174957.GX30522@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20180602174957.GX30522@ZenIV.linux.org.uk> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On Sat, Jun 02, 2018 at 06:49:58PM +0100, Al Viro wrote: > > > Hell, might even add AT_UMOUNT for "open root and detach, to be dissolved on > > > close", incompatible with AT_CLONE. > > > > Cute. Guess you could do: > > > > fd = open_mount(..., OPEN_TREE_DETACH); > > mount_setattr(fd, "", > > MOUNT_SETATTR_EMPTY_PATH, > > MOUNT_SETATTR_NOSUID, NULL); > > move_mount(fd, "", ...); Hadn't added that yet, but as for the rest of open_tree() - see vfs.git#mount-open_tree. open() and its flags are not touched at all. Other changes compared to the previous: * may_mount() is required for OPEN_TREE_CLONE * sys_ni.c cruft is dropped - those make no sense until and unless those syscalls become conditional. Appears to work, combined with move_mount() it yields eqiuvalents of mount --{move,bind,rbind}. Combined with mount_setattr(2) (when that gets added) we'll get mount -o remount,bind,nodev et.al. (including the currently absent whole-subtree versions) and mount --make-{r,}{shared,slave,private,unbindable} It also can be used to get an isolated subtree usable for ....at() stuff. The addition of syscall itself is done by the following and I'd really like linux-abi folks to comment on that puppy commit 6cfba4dd99b10278c2156c8d4fced2eddedf167f Author: Al Viro Date: Sat Jun 2 19:42:22 2018 -0400 new syscall: open_tree(2) open_tree(dfd, pathname, flags) Returns an O_PATH-opened file descriptor or an error. dfd and pathname specify the location to open, in usual fashion (see e.g. fstatat(2)). flags should be an OR of some of the following: * AT_PATH_EMPTY, AT_NO_AUTOMOUNT, AT_SYMLINK_NOFOLLOW - same meanings as usual * OPEN_TREE_CLOEXEC - make the resulting descriptor close-on-exec * OPEN_TREE_CLONE or OPEN_TREE_CLONE | AT_RECURSIVE - instead of opening the location in question, create a detached mount tree matching the subtree rooted at location specified by dfd/pathname. With AT_RECURSIVE the entire subtree is cloned, without it - only the part within in the mount containing the location in question. In other words, the same as mount --rbind or mount --bind would've taken. The detached tree will be dissolved on the final close of obtained file. Creation of such detached trees requires the same capabilities as doing mount --bind. Signed-off-by: Al Viro diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl index 14a2f996e543..b2b44ecd2b17 100644 --- a/arch/x86/entry/syscalls/syscall_32.tbl +++ b/arch/x86/entry/syscalls/syscall_32.tbl @@ -397,3 +397,4 @@ 383 i386 statx sys_statx __ia32_sys_statx 384 i386 arch_prctl sys_arch_prctl __ia32_compat_sys_arch_prctl 385 i386 io_pgetevents sys_io_pgetevents __ia32_compat_sys_io_pgetevents +391 i386 open_tree sys_open_tree __ia32_sys_open_tree diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl index cd36232ab62f..d6f4949378e7 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -342,6 +342,7 @@ 331 common pkey_free __x64_sys_pkey_free 332 common statx __x64_sys_statx 333 common io_pgetevents __x64_sys_io_pgetevents +339 common open_tree __x64_sys_open_tree # # x32-specific system call numbers start at 512 to avoid cache impact diff --git a/fs/file_table.c b/fs/file_table.c index 7ec0b3e5f05d..7480271a0d21 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -189,6 +189,7 @@ static void __fput(struct file *file) struct dentry *dentry = file->f_path.dentry; struct vfsmount *mnt = file->f_path.mnt; struct inode *inode = file->f_inode; + fmode_t mode = file->f_mode; might_sleep(); @@ -209,14 +210,14 @@ static void __fput(struct file *file) file->f_op->release(inode, file); security_file_free(file); if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL && - !(file->f_mode & FMODE_PATH))) { + !(mode & FMODE_PATH))) { cdev_put(inode->i_cdev); } fops_put(file->f_op); put_pid(file->f_owner.pid); - if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) + if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) i_readcount_dec(inode); - if (file->f_mode & FMODE_WRITER) { + if (mode & FMODE_WRITER) { put_write_access(inode); __mnt_drop_write(mnt); } @@ -224,6 +225,8 @@ static void __fput(struct file *file) file->f_path.mnt = NULL; file->f_inode = NULL; file_free(file); + if (unlikely(mode & FMODE_NEED_UNMOUNT)) + dissolve_on_fput(mnt); dput(dentry); mntput(mnt); } diff --git a/fs/internal.h b/fs/internal.h index 980d005b21b4..b55575b9b55c 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -85,6 +85,7 @@ extern void __mnt_drop_write(struct vfsmount *); extern void __mnt_drop_write_file(struct file *); extern void mnt_drop_write_file_path(struct file *); +extern void dissolve_on_fput(struct vfsmount *); /* * fs_struct.c */ diff --git a/fs/namespace.c b/fs/namespace.c index 5f75969adff1..3281fea98cf0 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -20,12 +20,14 @@ #include /* init_rootfs */ #include /* get_fs_root et.al. */ #include /* fsnotify_vfsmount_delete */ +#include #include #include #include #include #include #include +#include #include "pnode.h" #include "internal.h" @@ -1839,6 +1841,16 @@ struct vfsmount *collect_mounts(const struct path *path) return &tree->mnt; } +void dissolve_on_fput(struct vfsmount *mnt) +{ + namespace_lock(); + lock_mount_hash(); + mntget(mnt); + umount_tree(real_mount(mnt), UMOUNT_SYNC); + unlock_mount_hash(); + namespace_unlock(); +} + void drop_collected_mounts(struct vfsmount *mnt) { namespace_lock(); @@ -2198,6 +2210,30 @@ static bool has_locked_children(struct mount *mnt, struct dentry *dentry) return false; } +static struct mount *__do_loopback(struct path *old_path, int recurse) +{ + struct mount *mnt = ERR_PTR(-EINVAL), *old = real_mount(old_path->mnt); + + if (IS_MNT_UNBINDABLE(old)) + return mnt; + + if (!check_mnt(old) && old_path->dentry->d_op != &ns_dentry_operations) + return mnt; + + if (!recurse && has_locked_children(old, old_path->dentry)) + return mnt; + + if (recurse) + mnt = copy_tree(old, old_path->dentry, CL_COPY_MNT_NS_FILE); + else + mnt = clone_mnt(old, old_path->dentry, 0); + + if (!IS_ERR(mnt)) + mnt->mnt.mnt_flags &= ~MNT_LOCKED; + + return mnt; +} + /* * do loopback mount. */ @@ -2205,7 +2241,7 @@ static int do_loopback(struct path *path, const char *old_name, int recurse) { struct path old_path; - struct mount *mnt = NULL, *old, *parent; + struct mount *mnt = NULL, *parent; struct mountpoint *mp; int err; if (!old_name || !*old_name) @@ -2219,38 +2255,21 @@ static int do_loopback(struct path *path, const char *old_name, goto out; mp = lock_mount(path); - err = PTR_ERR(mp); - if (IS_ERR(mp)) + if (IS_ERR(mp)) { + err = PTR_ERR(mp); goto out; + } - old = real_mount(old_path.mnt); parent = real_mount(path->mnt); - - err = -EINVAL; - if (IS_MNT_UNBINDABLE(old)) - goto out2; - if (!check_mnt(parent)) goto out2; - if (!check_mnt(old) && old_path.dentry->d_op != &ns_dentry_operations) - goto out2; - - if (!recurse && has_locked_children(old, old_path.dentry)) - goto out2; - - if (recurse) - mnt = copy_tree(old, old_path.dentry, CL_COPY_MNT_NS_FILE); - else - mnt = clone_mnt(old, old_path.dentry, 0); - + mnt = __do_loopback(&old_path, recurse); if (IS_ERR(mnt)) { err = PTR_ERR(mnt); goto out2; } - mnt->mnt.mnt_flags &= ~MNT_LOCKED; - err = graft_tree(mnt, parent, mp); if (err) { lock_mount_hash(); @@ -2264,6 +2283,75 @@ static int do_loopback(struct path *path, const char *old_name, return err; } +SYSCALL_DEFINE3(open_tree, int, dfd, const char *, filename, unsigned, flags) +{ + struct file *file; + struct path path; + int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW; + bool detached = flags & OPEN_TREE_CLONE; + int error; + int fd; + + BUILD_BUG_ON(OPEN_TREE_CLOEXEC != O_CLOEXEC); + + if (flags & ~(AT_EMPTY_PATH | AT_NO_AUTOMOUNT | AT_RECURSIVE | + AT_SYMLINK_NOFOLLOW | OPEN_TREE_CLONE | + OPEN_TREE_CLOEXEC)) + return -EINVAL; + + if ((flags & (AT_RECURSIVE | OPEN_TREE_CLONE)) == AT_RECURSIVE) + return -EINVAL; + + if (flags & AT_NO_AUTOMOUNT) + lookup_flags &= ~LOOKUP_AUTOMOUNT; + if (flags & AT_SYMLINK_NOFOLLOW) + lookup_flags &= ~LOOKUP_FOLLOW; + if (flags & AT_EMPTY_PATH) + lookup_flags |= LOOKUP_EMPTY; + + if (detached && !may_mount()) + return -EPERM; + + fd = get_unused_fd_flags(flags & O_CLOEXEC); + if (fd < 0) + return fd; + + error = user_path_at(dfd, filename, lookup_flags, &path); + if (error) + goto out; + + if (detached) { + struct mount *mnt = __do_loopback(&path, flags & AT_RECURSIVE); + if (IS_ERR(mnt)) { + error = PTR_ERR(mnt); + goto out2; + } + mntput(path.mnt); + path.mnt = &mnt->mnt; + } + + file = dentry_open(&path, O_PATH, current_cred()); + if (IS_ERR(file)) { + error = PTR_ERR(file); + goto out3; + } + + if (detached) + file->f_mode |= FMODE_NEED_UNMOUNT; + path_put(&path); + fd_install(fd, file); + return fd; + +out3: + if (detached) + dissolve_on_fput(path.mnt); +out2: + path_put(&path); +out: + put_unused_fd(fd); + return error; +} + static int change_mount_flags(struct vfsmount *mnt, int ms_flags) { int error = 0; diff --git a/include/linux/fs.h b/include/linux/fs.h index 482563fe549c..706b4605bc26 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -154,6 +154,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset, /* File is capable of returning -EAGAIN if I/O will block */ #define FMODE_NOWAIT ((__force fmode_t)0x8000000) +/* File represents mount that needs unmounting */ +#define FMODE_NEED_UNMOUNT ((__force fmode_t)0x10000000) + /* * Flag for rw_copy_check_uvector and compat_rw_copy_check_uvector * that indicates that they should check the contents of the iovec are diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 811172fcb916..925483aba03a 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -896,7 +896,7 @@ asmlinkage long sys_pkey_alloc(unsigned long flags, unsigned long init_val); asmlinkage long sys_pkey_free(int pkey); asmlinkage long sys_statx(int dfd, const char __user *path, unsigned flags, unsigned mask, struct statx __user *buffer); - +asmlinkage long sys_open_tree(int dfd, const char __user *path, unsigned flags); /* * Architecture-specific system calls diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h index 6448cdd9a350..594b85f7cb86 100644 --- a/include/uapi/linux/fcntl.h +++ b/include/uapi/linux/fcntl.h @@ -90,5 +90,7 @@ #define AT_STATX_FORCE_SYNC 0x2000 /* - Force the attributes to be sync'd with the server */ #define AT_STATX_DONT_SYNC 0x4000 /* - Don't sync attributes with the server */ +#define AT_RECURSIVE 0x8000 /* Apply to the entire subtree */ + #endif /* _UAPI_LINUX_FCNTL_H */ diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h new file mode 100644 index 000000000000..b9c3b46210db --- /dev/null +++ b/include/uapi/linux/mount.h @@ -0,0 +1,7 @@ +#ifndef _UAPI_LINUX_MOUNT_H +#define _UAPI_LINUX_MOUNT_H + +#define OPEN_TREE_CLONE 1 +#define OPEN_TREE_CLOEXEC O_CLOEXEC + +#endif /* _UAPI_LINUX_MOUNT_H */