On 1/28/21 7:41 AM, Daniel Borkmann wrote:

On 1/27/21 5:23 AM, Bui Quang Minh wrote:

quoted

On Tue, Jan 26, 2021 at 09:36:57AM +0000, Lorenz Bauer wrote:

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On Tue, 26 Jan 2021 at 08:26, Bui Quang Minh 
[off-list ref] wrote:

quoted

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.

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* Seems like there are quite a few similar calls scattered around
(cpumap, etc.). Did you audit these as well?

[...]

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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.

quoted

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.