netdev - Re: [PATCH net] net: deal with integer overflows in kmalloc

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Message-ID: <CANn89iJtwNuLA2=dY-ZgLVtUrjt-K3K2gNv9XSt5Hyd2tV6+eQ@mail.gmail.com>
Date: Tue, 5 Sep 2023 14:27:08 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: David Laight <David.Laight@...lab.com>
Cc: Kyle Zeng <zengyhkyle@...il.com>, "David S . Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>, "eric.dumazet@...il.com" <eric.dumazet@...il.com>, 
	syzbot <syzkaller@...glegroups.com>, Kees Cook <keescook@...omium.org>, 
	Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH net] net: deal with integer overflows in kmalloc_reserve()

On Tue, Sep 5, 2023 at 10:36 AM David Laight <David.Laight@...lab.com> wrote:
>
> From: Eric Dumazet
> > Sent: 05 September 2023 04:42
> ...
> > Again, I do not want this patch, I want to fix the root cause(s).
> >
> > It makes no sense to allow dev->mtu to be as big as 0x7fffffff and
> > ultimately allow size to be bigger than 0x80000000
>
> kmem_alloc_reserve() also needs fixing.

Yes, this is what I said. Please provide a patch ?

I stopped caring about 32bit 10 years ago.

> It's purpose is to find the size that kmem_alloc() will
> allocated so that the full size can be allocated rather
> than later finding out the allocated size.
> The latter has issues with the compiler (etc) tracking
> the sizes of allocates.
>
> So it must never return a smaller size.
> Whether the path that returns 0 can happen or not
> the correct error return is the original size.
> The later kmalloc() will then probably fail and
> be checked for.
>
>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
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