2022-12-07 14:17:56

by Daniil Tatianin

Subject: [PATCH v1] drivers/vhost/vhost: fix overflow checks in vhost_overflow

The if statement would erroneously check for > ULONG_MAX, which could
never evaluate to true. Check for equality instead.

Found by Linux Verification Center (linuxtesting.org) with the SVACE
static analysis tool.

Signed-off-by: Daniil Tatianin <[email protected]>
---
drivers/vhost/vhost.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 40097826cff0..8df706e7bc6c 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -730,7 +730,7 @@ static bool log_access_ok(void __user *log_base, u64 addr, unsigned long sz)
/* Make sure 64 bit math will not overflow. */
static bool vhost_overflow(u64 uaddr, u64 size)
{
- if (uaddr > ULONG_MAX || size > ULONG_MAX)
+ if (uaddr == ULONG_MAX || size == ULONG_MAX)
return true;

if (!size)
--
2.25.1

2022-12-07 15:29:18

by Michael S. Tsirkin

Subject: Re: [PATCH v1] drivers/vhost/vhost: fix overflow checks in vhost_overflow

On Wed, Dec 07, 2022 at 04:46:31PM +0300, Daniil Tatianin wrote:
> The if statement would erroneously check for > ULONG_MAX, which could
> never evaluate to true. Check for equality instead.
>
> Found by Linux Verification Center (linuxtesting.org) with the SVACE
> static analysis tool.
>
> Signed-off-by: Daniil Tatianin <[email protected]>

It can trigger on a 32 bit system. I'd also expect more analysis
of the code flow than "this can not trigger switch to a condition
that can" to accompany a patch.

> ---
> drivers/vhost/vhost.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 40097826cff0..8df706e7bc6c 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -730,7 +730,7 @@ static bool log_access_ok(void __user *log_base, u64 addr, unsigned long sz)
> /* Make sure 64 bit math will not overflow. */
> static bool vhost_overflow(u64 uaddr, u64 size)
> {
> - if (uaddr > ULONG_MAX || size > ULONG_MAX)
> + if (uaddr == ULONG_MAX || size == ULONG_MAX)
> return true;
>
> if (!size)
> --
> 2.25.1

2022-12-08 07:52:28

by Daniil Tatianin

Subject: Re: [PATCH v1] drivers/vhost/vhost: fix overflow checks in vhost_overflow

On 12/7/22 6:01 PM, Michael S. Tsirkin wrote:
> On Wed, Dec 07, 2022 at 04:46:31PM +0300, Daniil Tatianin wrote:
>> The if statement would erroneously check for > ULONG_MAX, which could
>> never evaluate to true. Check for equality instead.
>>
>> Found by Linux Verification Center (linuxtesting.org) with the SVACE
>> static analysis tool.
>>
>> Signed-off-by: Daniil Tatianin <[email protected]>
>
> It can trigger on a 32 bit system. I'd also expect more analysis
> of the code flow than "this can not trigger switch to a condition
> that can" to accompany a patch.

Oops, my bad. It can trigger on 32 bit indeed. Sorry, completely
overlooked that.

Thanks

>> ---
>> drivers/vhost/vhost.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index 40097826cff0..8df706e7bc6c 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -730,7 +730,7 @@ static bool log_access_ok(void __user *log_base, u64 addr, unsigned long sz)
>> /* Make sure 64 bit math will not overflow. */
>> static bool vhost_overflow(u64 uaddr, u64 size)
>> {
>> - if (uaddr > ULONG_MAX || size > ULONG_MAX)
>> + if (uaddr == ULONG_MAX || size == ULONG_MAX)
>> return true;
>>
>> if (!size)
>> --
>> 2.25.1
>