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SubjectRe: [PATCH] vme: Fix integer overflow checking in vme_check_window()
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> On 30 Sep 2017, at 07:27, Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> The controversial part of this patch is that I've changed it so we now
> prevent integer overflows for VME_USER types and before we didn't. I
> view it as kernel-hardening. I looked at a couple places that used
> VME_USER types and they seemed pretty suspicious so I'm pretty sure
> preventing overflows here is a good idea.
>
> The most common problem which this function is for cases like VME_A16
> where we don't put an upper bound on "size" so you could have "size" set
> to U64_MAX and a valid vme_base would overflow the "vme_base + size"
> into the valid range as well.
>
> In the VME_A64 case, the integer overflow checking doesn't work because
> "U64_MAX + 1" has an integer overflow and it's just a complicated way of
> saying zero. That VME_A64 case is sort of interesting as well because
> there is a VME_A64_MAX define which is set to "U64_MAX + 1". The
> compiler will never let anyone use it since it can't be stored in a u64
> variable... With my patch it's now limited to just U64_MAX.
>
> Anyway, I put one integer overflow check at the start of the function
> and deleted all existing checks.
>
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Dmitry Kalinkin <dmitry.kalinkin@gmail.com>
>
> diff --git a/drivers/vme/vme.c b/drivers/vme/vme.c
> index 6a3ead42aba8..5b4c898d7509 100644
> --- a/drivers/vme/vme.c
> +++ b/drivers/vme/vme.c
> @@ -208,29 +208,27 @@ int vme_check_window(u32 aspace, unsigned long long vme_base,
> {
> int retval = 0;
>
> + if (vme_base + size < size)
> + return -EINVAL;
> +
> switch (aspace) {
> case VME_A16:
> - if (((vme_base + size) > VME_A16_MAX) ||
> - (vme_base > VME_A16_MAX))
> + if (vme_base + size > VME_A16_MAX)
> retval = -EFAULT;
> break;
> case VME_A24:
> - if (((vme_base + size) > VME_A24_MAX) ||
> - (vme_base > VME_A24_MAX))
> + if (vme_base + size > VME_A24_MAX)
> retval = -EFAULT;
> break;
> case VME_A32:
> - if (((vme_base + size) > VME_A32_MAX) ||
> - (vme_base > VME_A32_MAX))
> + if (vme_base + size > VME_A32_MAX)
> retval = -EFAULT;
> break;
> case VME_A64:
> - if ((size != 0) && (vme_base > U64_MAX + 1 - size))
> - retval = -EFAULT;
> + /* The VME_A64_MAX limit is actually U64_MAX + 1 */
> break;
> case VME_CRCSR:
> - if (((vme_base + size) > VME_CRCSR_MAX) ||
> - (vme_base > VME_CRCSR_MAX))
> + if (vme_base + size > VME_CRCSR_MAX)
> retval = -EFAULT;
> break;
> case VME_USER1:

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