From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: [PATCH 01/38] vfs: syscall: Add open_tree(2) to reference or clone a mount [ver #10] From: David Howells To: viro@zeniv.linux.org.uk Cc: linux-api@vger.kernel.org, torvalds@linux-foundation.org, dhowells@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 27 Jul 2018 18:31:30 +0100 Message-ID: <153271269067.9458.203758938391920203.stgit@warthog.procyon.org.uk> In-Reply-To: <153271267980.9458.7640156373438016898.stgit@warthog.procyon.org.uk> References: <153271267980.9458.7640156373438016898.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: From: Al Viro 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 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/file_table.c | 9 +- fs/internal.h | 1 fs/namespace.c | 132 +++++++++++++++++++++++++++----- include/linux/fs.h | 3 + include/linux/syscalls.h | 1 include/uapi/linux/fcntl.h | 2 include/uapi/linux/mount.h | 10 ++ 9 files changed, 135 insertions(+), 25 deletions(-) create mode 100644 include/uapi/linux/mount.h diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl index 3cf7b533b3d1..ea1b413afd47 100644 --- a/arch/x86/entry/syscalls/syscall_32.tbl +++ b/arch/x86/entry/syscalls/syscall_32.tbl @@ -398,3 +398,4 @@ 384 i386 arch_prctl sys_arch_prctl __ia32_compat_sys_arch_prctl 385 i386 io_pgetevents sys_io_pgetevents __ia32_compat_sys_io_pgetevents 386 i386 rseq sys_rseq __ia32_sys_rseq +387 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 f0b1709a5ffb..0545bed581dc 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -343,6 +343,7 @@ 332 common statx __x64_sys_statx 333 common io_pgetevents __x64_sys_io_pgetevents 334 common rseq __x64_sys_rseq +335 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 56533b08532e..383ee4724f77 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 03cc3b5bcf00..a4a01ecbcacd 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" @@ -1840,6 +1842,16 @@ 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(); @@ -2199,6 +2211,30 @@ 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. */ @@ -2206,7 +2242,7 @@ 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) @@ -2220,38 +2256,21 @@ 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(); @@ -2265,6 +2284,75 @@ 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 e3a18cddb74e..067f0e31aec7 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 73810808cdf2..3cc6b8f8bd2f 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -900,6 +900,7 @@ asmlinkage long sys_statx(int dfd, const char __user *path, unsigned flags, unsigned mask, struct statx __user *buffer); asmlinkage long sys_rseq(struct rseq __user *rseq, uint32_t rseq_len, int flags, uint32_t sig); +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..e8db2911adca --- /dev/null +++ b/include/uapi/linux/mount.h @@ -0,0 +1,10 @@ +#ifndef _UAPI_LINUX_MOUNT_H +#define _UAPI_LINUX_MOUNT_H + +/* + * open_tree() flags. + */ +#define OPEN_TREE_CLONE 1 /* Clone the target tree and attach the clone */ +#define OPEN_TREE_CLOEXEC O_CLOEXEC /* Close the file on execve() */ + +#endif /* _UAPI_LINUX_MOUNT_H */