From: Bui Quang Minh <minhquangbui99@gmail.com>
To: Daniel Borkmann <daniel@iogearbox.net>,
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: Mon, 17 May 2021 22:10:03 +0700 [thread overview]
Message-ID: <728b238e-a481-eb50-98e9-b0f430ab01e7@gmail.com> (raw)
In-Reply-To: <f4d20d92-2370-a8d3-d56c-408819a5f7f4@iogearbox.net>
On 1/28/21 7:41 AM, Daniel Borkmann wrote:
> 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").
Hi,
I almost forget about this patch, I have checked the bpf_map_area_alloc
in in stackmap.c and I can see that integer overflow cannot happen in
this stackmap.c case.
In stack_map_alloc(),
u64 cost;
...
cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);
cost += n_buckets * (value_size + sizeof(struct stack_map_bucket));
smap = bpf_map_area_alloc(cost, bpf_map_attr_numa_node(attr)); (1)
...
prealloc_elems_and_freelist(smap);
In prealloc_elems_and_freelist(),
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); (2)
Argument calculation at (1) is safe. Argument calculation at (2) can
potentially result in an integer overflow in 32-bit architecture.
However, if the integer overflow happens, it means argument at (1) must
be 2**32, which cannot pass the SIZE_MAX check in __bpf_map_area_alloc()
In __bpf_map_area_alloc()
if (size >= SIZE_MAX)
return NULL;
So I think the original patch has fixed instances of this bug pattern.
Thank you,
Quang Minh.
prev parent reply other threads:[~2021-05-17 16:27 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
2021-05-17 15:10 ` Bui Quang Minh [this message]
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