[Devel] [PATCH RHEL8 COMMIT] ms/vfs: syscall: Add open_tree(2) to reference or clone a mount
Konstantin Khorenko
khorenko at virtuozzo.com
Tue Sep 22 16:02:16 MSK 2020
The commit is pushed to "branch-rh8-4.18.0-193.6.3.vz8.4.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-193.6.3.vz8.4.6
------>
commit cd9f3d61b5bbf7ad81dbcba920834369b878b1a9
Author: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
Date: Tue Sep 22 16:02:16 2020 +0300
ms/vfs: syscall: Add open_tree(2) to reference or clone a mount
Patchset description:
These syscalls were added as preparation step for new mount api (fsopen,
fsconfig, fsmount and fspick will be ported separately).
We can use them to implement "cross-namespace bind-mounting" like this:
fd = open_tree(AT_FDCWD, "/mnt", OPEN_TREE_CLONE);
setns(nsfd, CLONE_NEWNS);
move_mount(fd, "", AT_FDCWD, "/mnt2", MOVE_MOUNT_F_EMPTY_PATH);
This will allow us implementing feature of adding bindmounts to runing
container instead of having unreliable external propagations.
Version for VZ8 is slightly different from VZ7 version.
https://jira.sw.ru/browse/PSBM-107263
Current patch description:
From: Al Viro <viro at zeniv.linux.org.uk>
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 <viro at zeniv.linux.org.uk>
Signed-off-by: David Howells <dhowells at redhat.com>
cc: linux-api at vger.kernel.org
Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
vfs: syscall: Add open_tree(2) to reference or clone a mount
(cherry-picked from commit a07b20004793d8926f78d63eb5980559f7813404)
uapi, x86: Fix the syscall numbering of the mount API syscalls [ver #2]
(cherry-picked from commit 9c8ad7a2ff0bfe58f019ec0abc1fb965114dde7d)
fs/namespace: add __user to open_tree and move_mount syscalls
(cherry-picked from commit 2658ce095df583cdf9ede475ec4da0b3cc7f7b05)
https://jira.sw.ru/browse/PSBM-107263
Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
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 | 3 +
include/linux/syscalls.h | 1 +
include/uapi/linux/fcntl.h | 1 +
include/uapi/linux/fs.h | 6 ++
9 files changed, 155 insertions(+), 25 deletions(-)
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 2eefd2a7c1ce..103079ec2891 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -401,3 +401,4 @@
425 i386 io_uring_setup sys_io_uring_setup __ia32_sys_io_uring_setup
426 i386 io_uring_enter sys_io_uring_enter __ia32_sys_io_uring_enter
427 i386 io_uring_register sys_io_uring_register __ia32_sys_io_uring_register
+428 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 65c026185e61..5772d5b0f1a6 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -346,6 +346,7 @@
425 common io_uring_setup __x64_sys_io_uring_setup
426 common io_uring_enter __x64_sys_io_uring_enter
427 common io_uring_register __x64_sys_io_uring_register
+428 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 2931252f47ae..4c8a5d845a1c 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -245,6 +245,7 @@ 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;
@@ -267,18 +268,20 @@ 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 e54ad4361d0d..c34bf7a1bb8b 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -83,6 +83,7 @@ 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 22589d59f476..a669502c450b 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -20,6 +20,7 @@
#include <linux/init.h> /* init_rootfs */
#include <linux/fs_struct.h> /* get_fs_root et.al. */
#include <linux/fsnotify.h> /* fsnotify_vfsmount_delete */
+#include <linux/file.h>
#include <linux/uaccess.h>
#include <linux/proc_ns.h>
#include <linux/magic.h>
@@ -1779,6 +1780,21 @@ 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();
@@ -2138,6 +2154,30 @@ 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.
*/
@@ -2145,7 +2185,7 @@ 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)
@@ -2159,38 +2199,21 @@ 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();
@@ -2204,6 +2227,96 @@ 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 __user *, 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;
+}
+
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 5fb43f9d7db2..a47765206391 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -167,6 +167,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
/* File does not contribute to nr_files count */
#define FMODE_NOACCOUNT ((__force fmode_t)0x20000000)
+/* 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 ed03cace6180..a282c957adcf 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -914,6 +914,7 @@ 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..dcb83fe2bbe4 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -90,5 +90,6 @@
#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/fs.h b/include/uapi/linux/fs.h
index 699ad890ac76..da2d0d0f989b 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -158,6 +158,12 @@ struct inodes_stat_t {
#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() */
+
/*
* Structure for FS_IOC_FSGETXATTR[A] and FS_IOC_FSSETXATTR.
*/
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