On Fri, 8 Feb 2019 at 22:27, Martin KaFai Lau <ka...@fb.com> wrote:
>
> By adding this test to test_verifier:
> {
> "reference tracking: access sk->src_ip4 (narrow load)",
> .insns = {
> BPF_SK_LOOKUP,
> BPF_MOV64_REG(BPF_REG_6, BPF_REG_0),
> BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 3),
> BPF_LDX_MEM(BPF_H, BPF_REG_2, BPF_REG_0, offsetof(struct bpf_sock,
> src_ip4) + 2),
> BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
> BPF_EMIT_CALL(BPF_FUNC_sk_release),
> BPF_EXIT_INSN(),
> },
> .prog_type = BPF_PROG_TYPE_SCHED_CLS,
> .result = ACCEPT,
> },
>
> The above test loads 2 bytes from sk->src_ip4 where
> sk is obtained by bpf_sk_lookup_tcp().
>
> It hits an internal verifier error from convert_ctx_accesses():
> [root@arch-fb-vm1 bpf]# ./test_verifier 665 665
> Failed to load prog 'Invalid argument'!
> 0: (b7) r2 = 0
> 1: (63) *(u32 *)(r10 -8) = r2
> 2: (7b) *(u64 *)(r10 -16) = r2
> 3: (7b) *(u64 *)(r10 -24) = r2
> 4: (7b) *(u64 *)(r10 -32) = r2
> 5: (7b) *(u64 *)(r10 -40) = r2
> 6: (7b) *(u64 *)(r10 -48) = r2
> 7: (bf) r2 = r10
> 8: (07) r2 += -48
> 9: (b7) r3 = 36
> 10: (b7) r4 = 0
> 11: (b7) r5 = 0
> 12: (85) call bpf_sk_lookup_tcp#84
> 13: (bf) r6 = r0
> 14: (15) if r0 == 0x0 goto pc+3
> R0=sock(id=1,off=0,imm=0) R6=sock(id=1,off=0,imm=0) R10=fp0,call_-1
> fp-8=????0000 fp-16=0000mmmm fp-24=mmmmmmmm fp-32=mmmmmmmm fp-40=mmmmmmmm
> fp-48=mmmmmmmm refs=1
> 15: (69) r2 = *(u16 *)(r0 +26)
> 16: (bf) r1 = r6
> 17: (85) call bpf_sk_release#86
> 18: (95) exit
>
> from 14 to 18: safe
> processed 20 insns (limit 131072), stack depth 48
> bpf verifier is misconfigured
> Summary: 0 PASSED, 0 SKIPPED, 1 FAILED
>
> The bpf_sock_is_valid_access() is expecting src_ip4 can be narrowly
> loaded (meaning load any 1 or 2 bytes of the src_ip4) by
> marking info->ctx_field_size. However, this marked
> ctx_field_size is not used. This patch fixes it.
>
> Due to the recent refactoring in test_verifier,
> this new test will be added to the bpf-next branch
> (together with the bpf_tcp_sock patchset)
> to avoid merge conflict.
>
> Fixes: c64b7983288e ("bpf: Add PTR_TO_SOCKET verifier type")
> Cc: Joe Stringer <j...@wand.net.nz>
> Signed-off-by: Martin KaFai Lau <ka...@fb.com>
> ---
Nice find, thanks.
Acked-by: Joe Stringer <j...@wand.net.nz>
