Messages in this thread | | | From | Alexander Lobakin <> | Subject | Re: [PATCH] ethtool: avoiding integer overflow in ethtool_phys_id() | Date | Mon, 21 Nov 2022 16:03:14 +0100 |
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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
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