From 8aa3af65b2b2a57bd40ecc47467d58d27cc9d3a7 Mon Sep 17 00:00:00 2001 From: Karel Zak Date: Wed, 27 May 2026 12:21:02 +0200 Subject: [PATCH 10/12] libmount: use fd_target in hook_idmap for move_mount() Use the pinned fd_target with MOVE_MOUNT_T_EMPTY_PATH for restricted users instead of string-based move_mount(). Re-open the target fd after mount to point to the mounted filesystem root. Signed-off-by: Karel Zak --- libmount/src/hook_idmap.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) Index: util-linux-2.40.4/libmount/src/hook_idmap.c =================================================================== --- util-linux-2.40.4.orig/libmount/src/hook_idmap.c +++ util-linux-2.40.4/libmount/src/hook_idmap.c @@ -349,10 +349,25 @@ static int hook_mount_post( /* Attach the idmapped mount. */ if (is_private) { + unsigned int mmflags = MOVE_MOUNT_F_EMPTY_PATH; + /* Unmount the old, non-idmapped mount we just cloned and idmapped. */ umount2(target, MNT_DETACH); - rc = move_mount(fd_tree, "", -1, target, MOVE_MOUNT_F_EMPTY_PATH); + if (mnt_context_target_fd_required(cxt)) { + int fd_tgt = mnt_context_get_target_fd(cxt); + + if (fd_tgt < 0) { + rc = -errno; + goto done; + } + mmflags |= MOVE_MOUNT_T_EMPTY_PATH; + rc = move_mount(fd_tree, "", fd_tgt, "", mmflags); + } else + rc = move_mount(fd_tree, "", AT_FDCWD, target, mmflags); + + if (rc == 0) + rc = mnt_context_reopen_target_fd(cxt); if (rc) DBG(HOOK, ul_debugobj(hs, " failed to set move mount")); }