bpf: reject stores into ctx via st and xadd

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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: d691f9e8d4 ("bpf: allow programs to write to certain skb fields")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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Daniel Borkmann 2018-01-16 23:30:10 +01:00 • committed by Alexei Starovoitov

parent a2284d912b

commit f37a8cb84c

2 changed files with 46 additions and 2 deletions

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19

kernel/bpf/verifier.c

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29

tools/testing/selftests/bpf/test_verifier.c

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