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Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH 01/10] vfs: syscall: Add open_tree(2) to reference or clone a mount From: David Howells To: viro@zeniv.linux.org.uk Cc: linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, dhowells@redhat.com, torvalds@linux-foundation.org, ebiederm@xmission.com, linux-security-module@vger.kernel.org Date: Tue, 19 Feb 2019 17:08:31 +0000 Message-ID: <155059611122.17079.12534811457233099094.stgit@warthog.procyon.org.uk> In-Reply-To: <155059610368.17079.2220554006494174417.stgit@warthog.procyon.org.uk> References: <155059610368.17079.2220554006494174417.stgit@warthog.procyon.org.uk> User-Agent: StGit/unknown-version MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Tue, 19 Feb 2019 17:08:33 +0000 (UTC) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: X-Virus-Scanned: ClamAV using ClamSMTP 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 Signed-off-by: Al Viro --- 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 | 157 ++++++++++++++++++++++++++++---- include/linux/fs.h | 7 + include/linux/syscalls.h | 1 include/uapi/linux/fcntl.h | 2 include/uapi/linux/mount.h | 6 + 9 files changed, 158 insertions(+), 27 deletions(-) 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 5679e7fcb6b0..10e0a3dcea4d 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -255,6 +255,7 @@ 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; if (unlikely(!(file->f_mode & FMODE_OPENED))) goto out; @@ -277,18 +278,20 @@ static void __fput(struct file *file) if (file->f_op->release) file->f_op->release(inode, 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); } dput(dentry); + if (unlikely(mode & FMODE_NEED_UNMOUNT)) + dissolve_on_fput(mnt); mntput(mnt); out: file_free(file); diff --git a/fs/internal.h b/fs/internal.h index 6a8b71643af4..f3a027c44758 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -94,6 +94,7 @@ extern int __mnt_want_write_file(struct file *); extern void __mnt_drop_write(struct vfsmount *); extern void __mnt_drop_write_file(struct file *); +extern void dissolve_on_fput(struct vfsmount *); /* * fs_struct.c */ diff --git a/fs/namespace.c b/fs/namespace.c index bb9b7db1c66c..112d46f26fc3 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -20,6 +20,7 @@ #include /* init_rootfs */ #include /* get_fs_root et.al. */ #include /* fsnotify_vfsmount_delete */ +#include #include #include #include @@ -1830,6 +1831,21 @@ struct vfsmount *collect_mounts(const struct path *path) return &tree->mnt; } +static void free_mnt_ns(struct mnt_namespace *); +static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *, bool); + +void dissolve_on_fput(struct vfsmount *mnt) +{ + struct mnt_namespace *ns; + namespace_lock(); + lock_mount_hash(); + ns = real_mount(mnt)->mnt_ns; + umount_tree(real_mount(mnt), UMOUNT_CONNECTED); + unlock_mount_hash(); + namespace_unlock(); + free_mnt_ns(ns); +} + void drop_collected_mounts(struct vfsmount *mnt) { namespace_lock(); @@ -2220,6 +2236,30 @@ 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. */ @@ -2227,7 +2267,7 @@ 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) @@ -2241,38 +2281,21 @@ 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(); @@ -2286,6 +2309,96 @@ static int do_loopback(struct path *path, const char *old_name, return err; } +static struct file *open_detached_copy(struct path *path, bool recursive) +{ + struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns; + struct mnt_namespace *ns = alloc_mnt_ns(user_ns, true); + struct mount *mnt, *p; + struct file *file; + + if (IS_ERR(ns)) + return ERR_CAST(ns); + + namespace_lock(); + mnt = __do_loopback(path, recursive); + if (IS_ERR(mnt)) { + namespace_unlock(); + free_mnt_ns(ns); + return ERR_CAST(mnt); + } + + lock_mount_hash(); + for (p = mnt; p; p = next_mnt(p, mnt)) { + p->mnt_ns = ns; + ns->mounts++; + } + ns->root = mnt; + list_add_tail(&ns->list, &mnt->mnt_list); + mntget(&mnt->mnt); + unlock_mount_hash(); + namespace_unlock(); + + mntput(path->mnt); + path->mnt = &mnt->mnt; + file = dentry_open(path, O_PATH, current_cred()); + if (IS_ERR(file)) + dissolve_on_fput(path->mnt); + else + file->f_mode |= FMODE_NEED_UNMOUNT; + return file; +} + +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 (unlikely(error)) { + file = ERR_PTR(error); + } else { + if (detached) + file = open_detached_copy(&path, flags & AT_RECURSIVE); + else + file = dentry_open(&path, O_PATH, current_cred()); + path_put(&path); + } + if (IS_ERR(file)) { + put_unused_fd(fd); + return PTR_ERR(file); + } + fd_install(fd, file); + return fd; +} + /* * Don't allow locked mount flags to be cleared. * diff --git a/include/linux/fs.h b/include/linux/fs.h index 3e85cb8e8c20..c4ef82689cab 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -159,10 +159,13 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset, #define FMODE_NONOTIFY ((__force fmode_t)0x4000000) /* File is capable of returning -EAGAIN if I/O will block */ -#define FMODE_NOWAIT ((__force fmode_t)0x8000000) +#define FMODE_NOWAIT ((__force fmode_t)0x8000000) + +/* File represents mount that needs unmounting */ +#define FMODE_NEED_UNMOUNT ((__force fmode_t)0x10000000) /* File does not contribute to nr_files count */ -#define FMODE_NOACCOUNT ((__force fmode_t)0x20000000) +#define FMODE_NOACCOUNT ((__force fmode_t)0x20000000) /* * Flag for rw_copy_check_uvector and compat_rw_copy_check_uvector diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 257cccba3062..07bca6796498 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -926,6 +926,7 @@ 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 index 3f9ec42510b0..fd7ae2e7eccf 100644 --- a/include/uapi/linux/mount.h +++ b/include/uapi/linux/mount.h @@ -55,4 +55,10 @@ #define MS_MGC_VAL 0xC0ED0000 #define MS_MGC_MSK 0xffff0000 +/* + * 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 */