Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.2 32/61] bpf, array: fix heap out-of-bounds access when updating elements | Date | Sat, 12 Dec 2015 12:06:00 -0800 |
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4.2-stable review patch. If anyone has any objections, please let me know.
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From: Daniel Borkmann <daniel@iogearbox.net>
[ Upstream commit fbca9d2d35c6ef1b323fae75cc9545005ba25097 ]
During own review but also reported by Dmitry's syzkaller [1] it has been noticed that we trigger a heap out-of-bounds access on eBPF array maps when updating elements. This happens with each map whose map->value_size (specified during map creation time) is not multiple of 8 bytes.
In array_map_alloc(), elem_size is round_up(attr->value_size, 8) and used to align array map slots for faster access. However, in function array_map_update_elem(), we update the element as ...
memcpy(array->value + array->elem_size * index, value, array->elem_size);
... where we access 'value' out-of-bounds, since it was allocated from map_update_elem() from syscall side as kmalloc(map->value_size, GFP_USER) and later on copied through copy_from_user(value, uvalue, map->value_size). Thus, up to 7 bytes, we can access out-of-bounds.
Same could happen from within an eBPF program, where in worst case we access beyond an eBPF program's designated stack.
Since 1be7f75d1668 ("bpf: enable non-root eBPF programs") didn't hit an official release yet, it only affects priviledged users.
In case of array_map_lookup_elem(), the verifier prevents eBPF programs from accessing beyond map->value_size through check_map_access(). Also from syscall side map_lookup_elem() only copies map->value_size back to user, so nothing could leak.
[1] http://github.com/google/syzkaller
Fixes: 28fbcfa08d8e ("bpf: add array type of eBPF maps") Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- kernel/bpf/arraymap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/bpf/arraymap.c +++ b/kernel/bpf/arraymap.c @@ -104,7 +104,7 @@ static int array_map_update_elem(struct /* all elements already exist */ return -EEXIST; - memcpy(array->value + array->elem_size * index, value, array->elem_size); + memcpy(array->value + array->elem_size * index, value, map->value_size); return 0; }
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