linux-kernel - Re: [PATCH] Fix compat regression in process_vm

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Date:   Mon, 26 Oct 2020 17:47:45 -0700
From:   Kyle Huey <me@...ehuey.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH] Fix compat regression in process_vm_rw()

On Mon, Oct 26, 2020 at 5:03 PM Jens Axboe <axboe@...nel.dk> wrote:
>
> The removal of compat_process_vm_{readv,writev} didn't change
> process_vm_rw(), which always assumes it's not doing a compat syscall.
> Instead of passing in 'false' unconditionally for 'compat', make it
> conditional on in_compat_syscall().
>
> Fixes: c3973b401ef2 ("mm: remove compat_process_vm_{readv,writev}")
> Reported-by: Kyle Huey <me@...ehuey.com>
> Signed-off-by: Jens Axboe <axboe@...nel.dk>
>
> ---
>
> diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
> index fd12da80b6f2..05676722d9cd 100644
> --- a/mm/process_vm_access.c
> +++ b/mm/process_vm_access.c
> @@ -273,7 +273,8 @@ static ssize_t process_vm_rw(pid_t pid,
>                 return rc;
>         if (!iov_iter_count(&iter))
>                 goto free_iov_l;
> -       iov_r = iovec_from_user(rvec, riovcnt, UIO_FASTIOV, iovstack_r, false);
> +       iov_r = iovec_from_user(rvec, riovcnt, UIO_FASTIOV, iovstack_r,
> +                               in_compat_syscall());
>         if (IS_ERR(iov_r)) {
>                 rc = PTR_ERR(iov_r);
>                 goto free_iov_l;
>
> --
> Jens Axboe
>

I tested this patch and it does fix the original testcase I reported.

- Kyle