Messages in this thread | | | Subject | Re: [PATCH] bpf: Fix integer overflow in argument calculation for bpf_map_area_alloc | From | Daniel Borkmann <> | Date | Thu, 28 Jan 2021 01:41:34 +0100 |
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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
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