[PATCH] ethtool: avoiding integer overflow in ethtool_phys_id()

[PATCH] ethtool: avoiding integer overflow in ethtool_phys_id()

[Maxim Korotkov]

The value of an arithmetic expression "n * id.data" is subject
to possible overflow due to a failure to cast operands to a larger data
type before performing arithmetic. Added cast of first operand to u64
for avoiding overflow.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 2adc6edcaec0 ("ethtool: fix error handling in ethtool_phys_id")
Signed-off-by: Maxim Korotkov <korotkov.maxim.s@gmail.com>
---
 net/ethtool/ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index 6a7308de192d..cf87e53c2e74 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c
@@ -2007,7 +2007,7 @@ static int ethtool_phys_id(struct net_device *dev, void __user *useraddr)
 	} else {
 		/* Driver expects to be called at twice the frequency in rc */
 		int n = rc * 2, interval = HZ / n;
-		u64 count = n * id.data, i = 0;
+		u64 count = (u64)n * id.data, i = 0;
 
 		do {
 			rtnl_lock();
-- 
2.17.1

Re: [PATCH] ethtool: avoiding integer overflow in ethtool_phys_id()

[Andrew Lunn]

On Mon, Nov 21, 2022 at 10:56:18AM +0300, Maxim Korotkov wrote:
> The value of an arithmetic expression "n * id.data" is subject
> to possible overflow due to a failure to cast operands to a larger data
> type before performing arithmetic. Added cast of first operand to u64
> for avoiding overflow.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: 2adc6edcaec0 ("ethtool: fix error handling in ethtool_phys_id")
> Signed-off-by: Maxim Korotkov <korotkov.maxim.s@gmail.com>
> ---
>  net/ethtool/ioctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
> index 6a7308de192d..cf87e53c2e74 100644
> --- a/net/ethtool/ioctl.c
> +++ b/net/ethtool/ioctl.c
> @@ -2007,7 +2007,7 @@ static int ethtool_phys_id(struct net_device *dev, void __user *useraddr)
>  	} else {
>  		/* Driver expects to be called at twice the frequency in rc */
>  		int n = rc * 2, interval = HZ / n;
> -		u64 count = n * id.data, i = 0;
> +		u64 count = (u64)n * id.data, i = 0;


How about moving the code around a bit, change n to a u64 and drop the
cast? Does this look correct?

		int interval = HZ / rc / 2;
		u64 n = rc * 2;
		u64 count = n * id.data;

		i = 0;

I just don't like casts, they suggest the underlying types are wrong,
so should fix that, not add a cast.

	Andrew

Re: [PATCH] ethtool: avoiding integer overflow in ethtool_phys_id()

[Alexander Lobakin]

From: Andrew Lunn <andrew@lunn.ch>
Date: Mon, 21 Nov 2022 15:10:18 +0100

> On Mon, Nov 21, 2022 at 10:56:18AM +0300, Maxim Korotkov wrote:
> > The value of an arithmetic expression "n * id.data" is subject
> > to possible overflow due to a failure to cast operands to a larger data
> > type before performing arithmetic. Added cast of first operand to u64
> > for avoiding overflow.
> > 
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> > 
> > Fixes: 2adc6edcaec0 ("ethtool: fix error handling in ethtool_phys_id")
> > Signed-off-by: Maxim Korotkov <korotkov.maxim.s@gmail.com>
> > ---
> >  net/ethtool/ioctl.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
> > index 6a7308de192d..cf87e53c2e74 100644
> > --- a/net/ethtool/ioctl.c
> > +++ b/net/ethtool/ioctl.c
> > @@ -2007,7 +2007,7 @@ static int ethtool_phys_id(struct net_device *dev, void __user *useraddr)
> >  	} else {
> >  		/* Driver expects to be called at twice the frequency in rc */
> >  		int n = rc * 2, interval = HZ / n;
> > -		u64 count = n * id.data, i = 0;
> > +		u64 count = (u64)n * id.data, i = 0;
> 
> 
> How about moving the code around a bit, change n to a u64 and drop the
> cast? Does this look correct?
> 
> 		int interval = HZ / rc / 2;
> 		u64 n = rc * 2;
> 		u64 count = n * id.data;
> 
> 		i = 0;
> 
> I just don't like casts, they suggest the underlying types are wrong,
> so should fix that, not add a cast.

This particular one is absolutely fine. When you want to multiply
u32 by u32, you always need a cast, otherwise the result will be
truncated. mul_u32_u32() does it the very same way[0].

> 
> 	Andrew
> 

[0] https://elixir.bootlin.com/linux/v6.1-rc6/source/include/linux/math64.h#L153

Thanks,
Olek

RE: [PATCH] ethtool: avoiding integer overflow in ethtool_phys_id()

[Keller, Jacob E]

> -----Original Message-----
> From: Alexander Lobakin <alexandr.lobakin@intel.com>
> Sent: Monday, November 21, 2022 7:03 AM
> To: Andrew Lunn <andrew@lunn.ch>
> Cc: Lobakin, Alexandr <alexandr.lobakin@intel.com>; Maxim Korotkov
> <korotkov.maxim.s@gmail.com>; David S. Miller <davem@davemloft.net>; Eric
> Dumazet <edumazet@google.com>; Jakub Kicinski <kuba@kernel.org>; Paolo
> Abeni <pabeni@redhat.com>; Guangbin Huang
> <huangguangbin2@huawei.com>; Tom Rix <trix@redhat.com>; Marco Bonelli
> <marco@mebeim.net>; Edward Cree <ecree@solarflare.com>;
> netdev@vger.kernel.org; linux-kernel@vger.kernel.org; lvc-
> project@linuxtesting.org
> Subject: Re: [PATCH] ethtool: avoiding integer overflow in ethtool_phys_id()
> 
> From: Andrew Lunn <andrew@lunn.ch>
> Date: Mon, 21 Nov 2022 15:10:18 +0100
> 
> > On Mon, Nov 21, 2022 at 10:56:18AM +0300, Maxim Korotkov wrote:
> > > The value of an arithmetic expression "n * id.data" is subject
> > > to possible overflow due to a failure to cast operands to a larger data
> > > type before performing arithmetic. Added cast of first operand to u64
> > > for avoiding overflow.
> > >
> > > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> > >
> > > Fixes: 2adc6edcaec0 ("ethtool: fix error handling in ethtool_phys_id")
> > > Signed-off-by: Maxim Korotkov <korotkov.maxim.s@gmail.com>
> > > ---
> > >  net/ethtool/ioctl.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
> > > index 6a7308de192d..cf87e53c2e74 100644
> > > --- a/net/ethtool/ioctl.c
> > > +++ b/net/ethtool/ioctl.c
> > > @@ -2007,7 +2007,7 @@ static int ethtool_phys_id(struct net_device *dev,
> void __user *useraddr)
> > >  	} else {
> > >  		/* Driver expects to be called at twice the frequency in rc */
> > >  		int n = rc * 2, interval = HZ / n;
> > > -		u64 count = n * id.data, i = 0;
> > > +		u64 count = (u64)n * id.data, i = 0;
> >
> >
> > How about moving the code around a bit, change n to a u64 and drop the
> > cast? Does this look correct?
> >
> > 		int interval = HZ / rc / 2;
> > 		u64 n = rc * 2;
> > 		u64 count = n * id.data;
> >
> > 		i = 0;
> >
> > I just don't like casts, they suggest the underlying types are wrong,
> > so should fix that, not add a cast.
> 
> This particular one is absolutely fine. When you want to multiply
> u32 by u32, you always need a cast, otherwise the result will be
> truncated. mul_u32_u32() does it the very same way[0].
> 

Why not just use mul_u32_u32 then?

Thanks,
Jake

> >
> > 	Andrew
> >
> 
> [0] https://elixir.bootlin.com/linux/v6.1-
> rc6/source/include/linux/math64.h#L153
> 
> Thanks,
> Olek

Re: [PATCH] ethtool: avoiding integer overflow in ethtool_phys_id()

[Maxim Korotkov]

Ok, I'll replace cast to macro in patch V2

On 22.11.2022 00:30, Keller, Jacob E wrote:
> 
> 
>> -----Original Message-----
>> From: Alexander Lobakin <alexandr.lobakin@intel.com>
>> Sent: Monday, November 21, 2022 7:03 AM
>> To: Andrew Lunn <andrew@lunn.ch>
>> Cc: Lobakin, Alexandr <alexandr.lobakin@intel.com>; Maxim Korotkov
>> <korotkov.maxim.s@gmail.com>; David S. Miller <davem@davemloft.net>; Eric
>> Dumazet <edumazet@google.com>; Jakub Kicinski <kuba@kernel.org>; Paolo
>> Abeni <pabeni@redhat.com>; Guangbin Huang
>> <huangguangbin2@huawei.com>; Tom Rix <trix@redhat.com>; Marco Bonelli
>> <marco@mebeim.net>; Edward Cree <ecree@solarflare.com>;
>> netdev@vger.kernel.org; linux-kernel@vger.kernel.org; lvc-
>> project@linuxtesting.org
>> Subject: Re: [PATCH] ethtool: avoiding integer overflow in ethtool_phys_id()
>>
>> From: Andrew Lunn <andrew@lunn.ch>
>> Date: Mon, 21 Nov 2022 15:10:18 +0100
>>
>>> On Mon, Nov 21, 2022 at 10:56:18AM +0300, Maxim Korotkov wrote:
>>>> The value of an arithmetic expression "n * id.data" is subject
>>>> to possible overflow due to a failure to cast operands to a larger data
>>>> type before performing arithmetic. Added cast of first operand to u64
>>>> for avoiding overflow.
>>>>
>>>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>>>
>>>> Fixes: 2adc6edcaec0 ("ethtool: fix error handling in ethtool_phys_id")
>>>> Signed-off-by: Maxim Korotkov <korotkov.maxim.s@gmail.com>
>>>> ---
>>>>   net/ethtool/ioctl.c | 2 +-
>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
>>>> index 6a7308de192d..cf87e53c2e74 100644
>>>> --- a/net/ethtool/ioctl.c
>>>> +++ b/net/ethtool/ioctl.c
>>>> @@ -2007,7 +2007,7 @@ static int ethtool_phys_id(struct net_device *dev,
>> void __user *useraddr)
>>>>    } else {
>>>>            /* Driver expects to be called at twice the frequency in rc */
>>>>            int n = rc * 2, interval = HZ / n;
>>>> -         u64 count = n * id.data, i = 0;
>>>> +         u64 count = (u64)n * id.data, i = 0;
>>>
>>>
>>> How about moving the code around a bit, change n to a u64 and drop the
>>> cast? Does this look correct?
>>>
>>>              int interval = HZ / rc / 2;
>>>              u64 n = rc * 2;
>>>              u64 count = n * id.data;
>>>
>>>              i = 0;
>>>
>>> I just don't like casts, they suggest the underlying types are wrong,
>>> so should fix that, not add a cast.
>>
>> This particular one is absolutely fine. When you want to multiply
>> u32 by u32, you always need a cast, otherwise the result will be
>> truncated. mul_u32_u32() does it the very same way[0].
>>
> 
> Why not just use mul_u32_u32 then?
> 
> Thanks,
> Jake
> 
>>>
>>>      Andrew
>>>
>>
>> [0] https://elixir.bootlin.com/linux/v6.1-
>> rc6/source/include/linux/math64.h#L153
>>
>> Thanks,
>> Olek

Re: [PATCH] ethtool: avoiding integer overflow in ethtool_phys_id()

[Jakub Kicinski]

On Mon, 21 Nov 2022 10:56:18 +0300 Maxim Korotkov wrote:
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: 2adc6edcaec0 ("ethtool: fix error handling in ethtool_phys_id")

I'm leaning towards dropping the fixes tag, and applying to -next.
Drivers returning high enough rc to cause an overflow seems theoretical, 
and is pretty harmless. Please LMK if I'm missing something.