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

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Date: Tue, 5 Sep 2023 08:36:00 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Eric Dumazet' <edumazet@...gle.com>, Kyle Zeng <zengyhkyle@...il.com>
CC: "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()

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.
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

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