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@xxxxxxxxx> 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.
