Provide a system call by which a filesystem opened with fsopen() and
configured by a series of writes can be mounted:
int ret = fsmount(int fsfd, int dfd, const char *path,
unsigned int at_flags, unsigned int flags);
where fsfd is the fd returned by fsopen(), dfd, path and at_flags locate
the mountpoint and flags are the applicable MS_* flags. dfd can be
AT_FDCWD or an fd open to a directory.
In the event that fsmount() fails, it may be possible to get an error
message by calling read(). If no message is available, ENODATA will be
reported.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---
arch/x86/entry/syscalls/syscall_32.tbl | 1
arch/x86/entry/syscalls/syscall_64.tbl | 1
fs/namespace.c | 133 ++++++++++++++++++++++++++++++++
include/linux/fs_context.h | 2
include/linux/syscalls.h | 2
include/uapi/linux/fs.h | 7 ++
kernel/sys_ni.c | 1
7 files changed, 147 insertions(+)
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 0e084cc11638..bdcb0c4a0491 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 fsopen sys_fsopen __ia32_sys_fsopen
+387 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 7200d5bb65ca..7d932d3897fa 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 fsopen __x64_sys_fsopen
+335 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 ead49e822418..03ade803b948 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3198,6 +3198,139 @@ struct vfsmount *kern_mount(struct file_system_type *type)
}
EXPORT_SYMBOL_GPL(kern_mount);
+/*
+ * Create a kernel mount representation for a new, prepared superblock
+ * (specified by fs_fd) and attach to an O_PATH-class file descriptor.
+ */
+SYSCALL_DEFINE5(fsmount, int, fs_fd, unsigned int, flags, unsigned int, ms_flags,
+ void *, spare_4, void *, spare_5)
+{
+ struct fs_context *fc;
+ struct inode *inode;
+ struct file *file;
+ struct path newmount;
+ struct fd f;
+ unsigned int mnt_flags = 0;
+ long ret;
+
+ if ((flags & ~(FSMOUNT_CLOEXEC)) != 0 || spare_4 || spare_5)
+ 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_fs_fops)
+ goto err_fsfd;
+
+ fc = f.file->private_data;
+
+ ret = -EPERM;
+ if (!may_mount() ||
+ ((fc->sb_flags & SB_MANDLOCK) && !may_mandlock()))
+ goto err_fsfd;
+
+ /* 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;
+ }
+
+ inode = file_inode(f.file);
+ ret = inode_lock_killable(inode);
+ if (ret < 0)
+ goto err_fsfd;
+
+ ret = -EBUSY;
+ if (fc->phase != FS_CONTEXT_AWAITING_MOUNT)
+ 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.
+ */
+ if (fc->ops && fc->ops->free)
+ fc->ops->free(fc);
+ fc->fs_private = NULL;
+ fc->s_fs_info = NULL;
+ fc->sb_flags = 0;
+ fc->sloppy = false;
+ fc->silent = false;
+ fc->source_is_dev = false;
+ security_fs_context_free(fc);
+ fc->security = NULL;
+ kfree(fc->subtype);
+ fc->subtype = NULL;
+ kfree(fc->source);
+ fc->source = NULL;
+
+ fc->purpose = FS_CONTEXT_FOR_RECONFIGURE;
+ fc->phase = FS_CONTEXT_AWAITING_RECONF;
+
+ /* 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))
+ goto err_path;
+ file->f_mode |= FMODE_NEED_UNMOUNT;
+
+ ret = get_unused_fd_flags(flags & FSMOUNT_CLOEXEC);
+ if (ret < 0)
+ goto err_file;
+
+ fd_install(ret, file);
+
+err_file:
+ fput(file);
+err_path:
+ path_put(&newmount);
+err_unlock:
+ inode_unlock(inode);
+err_fsfd:
+ fdput(f);
+ return ret;
+}
+
/*
* Return true if path is reachable from root
*
diff --git a/include/linux/fs_context.h b/include/linux/fs_context.h
index 368fe5bb1efd..bec4022e3f4b 100644
--- a/include/linux/fs_context.h
+++ b/include/linux/fs_context.h
@@ -115,4 +115,6 @@ extern int vfs_get_super(struct fs_context *fc,
int (*fill_super)(struct super_block *sb,
struct fs_context *fc));
+extern const struct file_operations fscontext_fs_fops;
+
#endif /* _LINUX_FS_CONTEXT_H */
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index e0f19406af92..178370cad1dd 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -898,6 +898,8 @@ asmlinkage long sys_statx(int dfd, const char __user *path, unsigned flags,
unsigned mask, struct statx __user *buffer);
asmlinkage long sys_fsopen(const char *fs_name, unsigned int flags,
void *reserved3, void *reserved4, void *reserved5);
+asmlinkage long sys_fsmount(int fsfd, int dfd, const char *path, unsigned int at_flags,
+ unsigned int flags);
/*
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 5da6c2d96af5..edb1983a9990 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -338,4 +338,11 @@ typedef int __bitwise __kernel_rwf_t;
#define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
RWF_APPEND)
+/*
+ * Flags for fsopen() and co.
+ */
+#define FSOPEN_CLOEXEC 0x00000001
+
+#define FSMOUNT_CLOEXEC 0x00000001
+
#endif /* _UAPI_LINUX_FS_H */
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 6bb0e1bb3eae..632a937ca09c 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -435,3 +435,4 @@ COND_SYSCALL(setuid16);
/* fd-based mount */
COND_SYSCALL(sys_fsopen);
+COND_SYSCALL(sys_fsmount);
