linux-kernel - Re: [PATCH v3] xen/privcmd: fix error exit of privcmd_ioctl_dm

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <744be7c4-8e00-7876-5819-a1d07d3d423f@suse.com>
Date:   Thu, 25 Aug 2022 13:58:59 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        stable@...r.kernel.org,
        Rustam Subkhankulov <subkhankulov@...ras.ru>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] xen/privcmd: fix error exit of privcmd_ioctl_dm_op()

On 25.08.2022 13:40, Juergen Gross wrote:
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -581,7 +581,7 @@ static int lock_pages(
>  	struct privcmd_dm_op_buf kbufs[], unsigned int num,
>  	struct page *pages[], unsigned int nr_pages, unsigned int *pinned)
>  {
> -	unsigned int i;
> +	unsigned int i, off = 0;
>  
>  	for (i = 0; i < num; i++) {
>  		unsigned int requested;
> @@ -589,19 +589,23 @@ static int lock_pages(
>  
>  		requested = DIV_ROUND_UP(
>  			offset_in_page(kbufs[i].uptr) + kbufs[i].size,
> -			PAGE_SIZE);
> +			PAGE_SIZE) - off;
>  		if (requested > nr_pages)
>  			return -ENOSPC;
>  
>  		page_count = pin_user_pages_fast(
> -			(unsigned long) kbufs[i].uptr,
> +			(unsigned long)kbufs[i].uptr + off * PAGE_SIZE,
>  			requested, FOLL_WRITE, pages);
> -		if (page_count < 0)
> -			return page_count;
> +		if (page_count <= 0)
> +			return page_count ? : -EFAULT;
>  
>  		*pinned += page_count;
>  		nr_pages -= page_count;
>  		pages += page_count;
> +
> +		off = requested - page_count;
> +		if (off)
> +			i--;
>  	}

Initially I thought this would go wrong only on the 3rd iteration, but
meanwhile I think it's wrong already on the 2nd. What I think you need
is

		if (page_count < requested)
			i--;
		off += page_count;

or with the i++ from the loop header absorbed here

		if (page_count == requested)
			i++;
		off += page_count;

Plus of course off needs resetting to zero whenever i advances. I.e.

		if (page_count == requested) {
			i++;
			off = 0;
		} else {
			off += page_count;
		}

Jan