Re: [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc

On Wed, Jan 27, 2021 at 11:23:41AM +0700, Bui Quang Minh wrote:

quoted

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

I spotted another bug after re-auditting. In hashtab, there ares 2 places using
the same calls

	static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
	{
		/* ... snip ... */
		if (htab->n_buckets == 0 ||
		    htab->n_buckets > U32_MAX / sizeof(struct bucket))
			goto free_htab;

		htab->buckets = bpf_map_area_alloc(htab->n_buckets *
						   sizeof(struct bucket),
						   htab->map.numa_node);
	}

This is safe because of the above check.

	static int prealloc_init(struct bpf_htab *htab)
	{
		u32 num_entries = htab->map.max_entries;
		htab->elems = bpf_map_area_alloc(htab->elem_size * num_entries,
						 htab->map.numa_node);
	}

This is not safe since there is no limit check in elem_size.

So sorry but I rechecked and saw this bug in hashtab has been fixed with commit
e1868b9e36d0ca

Thank you,
Quang Minh.