Re: [PATCH] net: fix compat pointer in get_compat_msghdr()

[Marek Szyprowski <m.szyprowski@samsung.com>]

On 16.07.2022 00:03, Jens Axboe wrote:
> A previous change enabled external users to copy the data before
> calling __get_compat_msghdr(), but didn't modify get_compat_msghdr() or
> __io_compat_recvmsg_copy_hdr() to take that into account. They are both
> stil passing in the __user pointer rather than the copied version.
>
> Ensure we pass in the kernel struct, not the pointer to the user data.
>
> Link: https://lore.kernel.org/all/46439555-644d-08a1-7d66-16f8f9a320f0@samsung.com/
> Fixes: 1a3e4e94a1b9 ("net: copy from user before calling __get_compat_msghdr")
> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>

This fixes the issue I've reported.

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

> ---
>
> As this was staged in the io_uring tree, I plan on applying this fix
> there as well. Holler if anyone disagrees.
>
> diff --git a/io_uring/net.c b/io_uring/net.c
> index 6b7d5f33e642..e61efa31c729 100644
> --- a/io_uring/net.c
> +++ b/io_uring/net.c
> @@ -398,7 +398,7 @@ static int __io_compat_recvmsg_copy_hdr(struct io_kiocb *req,
>   	if (copy_from_user(&msg, sr->umsg_compat, sizeof(msg)))
>   		return -EFAULT;
>   
> -	ret = __get_compat_msghdr(&iomsg->msg, sr->umsg_compat, &iomsg->uaddr);
> +	ret = __get_compat_msghdr(&iomsg->msg, &msg, &iomsg->uaddr);
>   	if (ret)
>   		return ret;
>   
> diff --git a/net/compat.c b/net/compat.c
> index 513aa9a3fc64..ed880729d159 100644
> --- a/net/compat.c
> +++ b/net/compat.c
> @@ -89,7 +89,7 @@ int get_compat_msghdr(struct msghdr *kmsg,
>   	if (copy_from_user(&msg, umsg, sizeof(*umsg)))
>   		return -EFAULT;
>   
> -	err = __get_compat_msghdr(kmsg, umsg, save_addr);
> +	err = __get_compat_msghdr(kmsg, &msg, save_addr);
>   	if (err)
>   		return err;
>   

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland