On 14/9/23 14:00, Amir Goldstein wrote:
On Wed, Sep 13, 2023 at 6:22 PM 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 old (32bit) or 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_64.tbl | 1 + fs/namespace.c | 51 ++++++++++++++++++++++++++ include/linux/syscalls.h | 2 + include/uapi/asm-generic/unistd.h | 5 ++- 4 files changed, 58 insertions(+), 1 deletion(-) diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl index 6d807c30cd16..0d9a47b0ce9b 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -376,6 +376,7 @@ 452 common fchmodat2 sys_fchmodat2 453 64 map_shadow_stack sys_map_shadow_stack 454 common statmnt sys_statmnt +455 common listmnt sys_listmnt # # Due to a historical design error, certain syscalls are numbered differently diff --git a/fs/namespace.c b/fs/namespace.c index 088a52043bba..5362b1ffb26f 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -4988,6 +4988,57 @@ SYSCALL_DEFINE5(statmnt, u64, mnt_id, return err; } +static long do_listmnt(struct vfsmount *mnt, u64 __user *buf, size_t bufsize, + const struct path *root) +{ + struct mount *r, *m = real_mount(mnt); + struct path rootmnt = { .mnt = root->mnt, .dentry = root->mnt->mnt_root }; + long ctr = 0; + + if (!capable(CAP_SYS_ADMIN) && + !is_path_reachable(m, mnt->mnt_root, &rootmnt)) + return -EPERM; + + list_for_each_entry(r, &m->mnt_mounts, mnt_child) { + if (!capable(CAP_SYS_ADMIN) && + !is_path_reachable(r, r->mnt.mnt_root, root)) + continue; + + if (ctr >= bufsize) + return -EOVERFLOW; + if (put_user(r->mnt_id_unique, buf + ctr)) + return -EFAULT; + ctr++; + if (ctr < 0) + return -ERANGE;I think it'd be good for userspace to be able to query required bufsize with NULL buf, listattr style, rather than having to guess and re-guess on EOVERFLOW.
Agreed, I also think that would be useful. Ian
