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From: Daniel Borkmann <daniel@iogearbox.net>
To: Bui Quang Minh <minhquangbui99@gmail.com>,
	Lorenz Bauer <lmb@cloudflare.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
	"David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	hawk@kernel.org, John Fastabend <john.fastabend@gmail.com>,
	Andrii Nakryiko <andrii@kernel.org>, Martin Lau <kafai@fb.com>,
	Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
	kpsingh@kernel.org, Jakub Sitnicki <jakub@cloudflare.com>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc
Date: Thu, 28 Jan 2021 01:41:34 +0100	[thread overview]
Message-ID: <f4d20d92-2370-a8d3-d56c-408819a5f7f4@iogearbox.net> (raw)
In-Reply-To: <20210127042341.GA4948@ubuntu>

On 1/27/21 5:23 AM, Bui Quang Minh wrote:
> On Tue, Jan 26, 2021 at 09:36:57AM +0000, Lorenz Bauer wrote:
>> On Tue, 26 Jan 2021 at 08:26, Bui Quang Minh <minhquangbui99@gmail.com> wrote:
>>>
>>> In 32-bit architecture, the result of sizeof() is a 32-bit integer so
>>> the expression becomes the multiplication between 2 32-bit integer which
>>> can potentially leads to integer overflow. As a result,
>>> bpf_map_area_alloc() allocates less memory than needed.
>>>
>>> Fix this by casting 1 operand to u64.
>>
>> Some quick thoughts:
>> * Should this have a Fixes tag?
> 
> Ok, I will add Fixes tag in later version patch.
> 
>> * Seems like there are quite a few similar calls scattered around
>> (cpumap, etc.). Did you audit these as well?
> 
[...]
> In cpumap,
> 
> 	static struct bpf_map *cpu_map_alloc(union bpf_attr *attr)
> 	{
> 		cmap->cpu_map = bpf_map_area_alloc(cmap->map.max_entries *
> 						   sizeof(struct bpf_cpu_map_entry *),
> 						   cmap->map.numa_node);
> 	}
> 
> I think this is safe because max_entries is not permitted to be larger than NR_CPUS.

Yes.

> In stackmap, there is a place that I'm not very sure about
> 
> 	static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
> 	{
> 		u32 elem_size = sizeof(struct stack_map_bucket) + smap->map.value_size;
> 		smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries,
> 						 smap->map.numa_node);
> 	}
> 
> This is called after another bpf_map_area_alloc in stack_map_alloc(). In the first
> bpf_map_area_alloc() the argument is calculated in an u64 variable; so if in the second
> one, there is an integer overflow then the first one must be called with size > 4GB. I
> think the first one will probably fail (I am not sure about the actual limit of vmalloc()),
> so the second one might not be called.

I would sanity check this as well. Looks like k*alloc()/v*alloc() call sites typically
use array_size() which returns SIZE_MAX on overflow, 610b15c50e86 ("overflow.h: Add
allocation size calculation helpers").

Thanks,
Daniel

  parent reply	other threads:[~2021-01-28  0:42 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-26  8:26 [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc Bui Quang Minh
2021-01-26  9:36 ` Lorenz Bauer
2021-01-27  4:23   ` Bui Quang Minh
2021-01-27  5:09     ` Bui Quang Minh
2021-01-28  0:41     ` Daniel Borkmann [this message]
2021-05-17 15:10       ` Bui Quang Minh

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