On Wed, Feb 21, 2024 at 06:30:50PM +0100, Jan Kara wrote:
> Avoid holding writeable fd to a loop device that is being mounted. In
> the hardened configurations (CONFIG_BLK_DEV_WRITE_MOUNTED = n) the
> kernel wants to make sure nobody else has the block device writeably
> open when mounting so this makes the mount fail.
>
> Reported-by: JunChao Sun <sunjunchao2870@xxxxxxxxx>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
Sounds good!
Acked-by: Christian Brauner <brauner@xxxxxxxxxx>
> libmount/src/hook_loopdev.c | 16 ++++++++++------
> 1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/libmount/src/hook_loopdev.c b/libmount/src/hook_loopdev.c
> index 8c8f7f218732..e2114b0cbebe 100644
> --- a/libmount/src/hook_loopdev.c
> +++ b/libmount/src/hook_loopdev.c
> @@ -356,15 +356,19 @@ success:
> */
> mnt_optlist_append_flags(ol, MS_RDONLY, cxt->map_linux);
>
> - /* we have to keep the device open until mount(1),
> - * otherwise it will be auto-cleared by kernel
> + /*
> + * We have to keep the device open until mount(1), otherwise it
> + * will be auto-cleared by kernel. However we don't want to
> + * keep writeable fd as kernel wants to block all writers to
> + * the device being mounted (in the more hardened
> + * configurations). So grab read-only fd instead.
> */
> - hd->loopdev_fd = loopcxt_get_fd(&lc);
> + hd->loopdev_fd = open(lc.device, O_RDONLY | O_CLOEXEC);
> if (hd->loopdev_fd < 0) {
> - DBG(LOOP, ul_debugobj(cxt, "failed to get loopdev FD"));
> + DBG(LOOP,
> + ul_debugobj(cxt, "failed to reopen loopdev FD"));
> rc = -errno;
> - } else
> - loopcxt_set_fd(&lc, -1, 0);
> + }
> }
> done:
> loopcxt_deinit(&lc);
> --
> 2.35.3
>
