Re: [PATCH bpf] bpf: reject stores into ctx via st and xadd

On Tue, Jan 16, 2018 at 11:30:10PM +0100, Daniel Borkmann wrote:

Alexei found that verifier does not reject stores into context
via BPF_ST instead of BPF_STX. And while looking at it, we
also should not allow XADD variant of BPF_STX.

The context rewriter is only assuming either BPF_LDX_MEM- or
BPF_STX_MEM-type operations, thus reject anything other than
that so that assumptions in the rewriter properly hold. Add
test cases as well for BPF selftests.

Fixes: d691f9e8d440 ("bpf: allow programs to write to certain skb fields")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Applied, thank you Daniel.

all bugs are eventually shallow.
For this one we even had two broken testcases. Ouch.