On Thu, Sep 28, 2023 at 9:04 AM Miklos Szeredi <mszeredi@xxxxxxxxxx> wrote:
>
> Add way to query the children of a particular mount. This is a more
> flexible way to iterate the mount tree than having to parse the complete
> /proc/self/mountinfo.
>
> Lookup the mount by the new 64bit mount ID. If a mount needs to be queried
> based on path, then statx(2) can be used to first query the mount ID
> belonging to the path.
>
> Return an array of new (64bit) mount ID's. Without privileges only mounts
> are listed which are reachable from the task's root.
>
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> ---
> arch/x86/entry/syscalls/syscall_32.tbl | 1 +
> arch/x86/entry/syscalls/syscall_64.tbl | 1 +
> fs/namespace.c | 69 ++++++++++++++++++++++++++
> include/linux/syscalls.h | 3 ++
> include/uapi/asm-generic/unistd.h | 5 +-
> include/uapi/linux/mount.h | 3 ++
> 6 files changed, 81 insertions(+), 1 deletion(-)
...
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 3326ba2b2810..050e2d2af110 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -4970,6 +4970,75 @@ SYSCALL_DEFINE4(statmount, const struct __mount_arg __user *, req,
> return ret;
> }
>
> +static long do_listmount(struct vfsmount *mnt, u64 __user *buf, size_t bufsize,
> + const struct path *root, unsigned int flags)
> +{
> + struct mount *r, *m = real_mount(mnt);
> + struct path rootmnt = {
> + .mnt = root->mnt,
> + .dentry = root->mnt->mnt_root
> + };
> + long ctr = 0;
> + bool reachable_only = true;
> + int err;
> +
> + err = security_sb_statfs(mnt->mnt_root);
> + if (err)
> + return err;
> +
> + if (flags & LISTMOUNT_UNREACHABLE) {
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> + reachable_only = false;
> + }
> +
> + if (reachable_only && !is_path_reachable(m, mnt->mnt_root, &rootmnt))
> + return capable(CAP_SYS_ADMIN) ? 0 : -EPERM;
> +
> + list_for_each_entry(r, &m->mnt_mounts, mnt_child) {
> + if (reachable_only &&
> + !is_path_reachable(r, r->mnt.mnt_root, root))
> + continue;
I believe we would want to move the security_sb_statfs() call from
above to down here; something like this I think ...
err = security_sb_statfs(r->mnt.mnt_root);
if (err)
/* if we can't access the mount, pretend it doesn't exist */
continue;
> + if (ctr >= bufsize)
> + return -EOVERFLOW;
> + if (put_user(r->mnt_id_unique, buf + ctr))
> + return -EFAULT;
> + ctr++;
> + if (ctr < 0)
> + return -ERANGE;
> + }
> + return ctr;
> +}
--
paul-moore.com
