Re: [PATCH bpf-next v2] bpf: Do not try bpf_msg_push_data with len 0

[Yonghong Song <yhs@fb.com>]

On 2/9/22 7:55 AM, Felix Maurer wrote:
> If bpf_msg_push_data is called with len 0 (as it happens during
> selftests/bpf/test_sockmap), we do not need to do anything and can
> return early.
> 
> Calling bpf_msg_push_data with len 0 previously lead to a wrong ENOMEM
> error: we later called get_order(copy + len); if len was 0, copy + len
> was also often 0 and get_order returned some undefined value (at the
> moment 52). alloc_pages caught that and failed, but then
> bpf_msg_push_data returned ENOMEM. This was wrong because we are most
> probably not out of memory and actually do not need any additional
> memory.
> 
> v2: Add bug description and Fixes tag
> 
> Fixes: 6fff607e2f14b ("bpf: sk_msg program helper bpf_msg_push_data")
> Signed-off-by: Felix Maurer <fmaurer@redhat.com>

LGTM. I am wondering why bpf CI didn't catch this problem. Did you
modified the test with length 0 in order to trigger that? If this
is the case, it would be great you can add such a test to the
test_sockmap.

Acked-by: Yonghong Song <yhs@fb.com>