Re: [PATCH] prctl: require checkpoint_restore_ns_capable for PR_SET_MM_MAP

[Oleg Nesterov]

On 04/02, Qi Tang wrote:
>
> The original commit f606b77f1a9e ("prctl: PR_SET_MM -- introduce
> PR_SET_MM_MAP operation") states "we require the caller to be at least
> user-namespace root user", but this was never enforced in the code.
>
> Add a checkpoint_restore_ns_capable() check at the top of
> prctl_set_mm_map(), after the PR_SET_MM_MAP_SIZE early return.  This
> requires CAP_CHECKPOINT_RESTORE or CAP_SYS_ADMIN in the caller's
> user namespace, matching the stated design intent and the existing
> check for exe_fd changes.

Can't really comment... but if you add this check at the start, then you
should also remove the same checkpoint_restore_ns_capable() check below?
In the "if (prctl_map.exe_fd != (u32)-1)" block.

Oleg.


> Fixes: f606b77f1a9e ("prctl: PR_SET_MM -- introduce PR_SET_MM_MAP operation")
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
> Signed-off-by: Qi Tang <tpluszz77@xxxxxxxxx>
> ---
>  kernel/sys.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/sys.c b/kernel/sys.c
> index c86eba9aa7e9..2b8c57f23a35 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2071,6 +2071,9 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data
>  		return put_user((unsigned int)sizeof(prctl_map),
>  				(unsigned int __user *)addr);
>  
> +	if (!checkpoint_restore_ns_capable(current_user_ns()))
> +		return -EPERM;
> +
>  	if (data_size != sizeof(prctl_map))
>  		return -EINVAL;
>  
> -- 
> 2.43.0
>