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bpf: improve verifier packet range checks

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llvm can optimize the 'if (ptr > data_end)' checks to be in the order
slightly different than the original C code which will confuse verifier.
Like:
if (ptr + 16 > data_end)
  return TC_ACT_SHOT;
// may be followed by
if (ptr + 14 > data_end)
  return TC_ACT_SHOT;
while llvm can see that 'ptr' is valid for all 16 bytes,
the verifier could not.
Fix verifier logic to account for such case and add a test.

Reported-by: Huapeng Zhou <hzhou@fb.com>
Fixes: 969bf05eb3 ("bpf: direct packet access")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov 2017-03-24 15:57:33 -07:00 committed by David S. Miller
parent 43a6684519
commit b1977682a3
2 changed files with 23 additions and 2 deletions
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5
kernel/bpf/verifier.c
View File

@ -1973,14 +1973,15 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *state,
for (i = 0; i < MAX_BPF_REG; i++) for (i = 0; i < MAX_BPF_REG; i++)
if (regs[i].type == PTR_TO_PACKET && regs[i].id == dst_reg->id) if (regs[i].type == PTR_TO_PACKET && regs[i].id == dst_reg->id)
regs[i].range = dst_reg->off; /* keep the maximum range already checked */
regs[i].range = max(regs[i].range, dst_reg->off);
for (i = 0; i < MAX_BPF_STACK; i += BPF_REG_SIZE) { for (i = 0; i < MAX_BPF_STACK; i += BPF_REG_SIZE) {
if (state->stack_slot_type[i] != STACK_SPILL) if (state->stack_slot_type[i] != STACK_SPILL)
continue; continue;
reg = &state->spilled_regs[i / BPF_REG_SIZE]; reg = &state->spilled_regs[i / BPF_REG_SIZE];
if (reg->type == PTR_TO_PACKET && reg->id == dst_reg->id) if (reg->type == PTR_TO_PACKET && reg->id == dst_reg->id)
reg->range = dst_reg->off; reg->range = max(reg->range, dst_reg->off);
} }
} }

20
tools/testing/selftests/bpf/test_verifier.c
View File

@ -3417,6 +3417,26 @@ static struct bpf_test tests[] = {
.result = ACCEPT, .result = ACCEPT,
.prog_type = BPF_PROG_TYPE_LWT_XMIT, .prog_type = BPF_PROG_TYPE_LWT_XMIT,
}, },
{
"overlapping checks for direct packet access",
.insns = {
BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,
offsetof(struct __sk_buff, data)),
BPF_LDX_MEM(BPF_W, BPF_REG_3, BPF_REG_1,
offsetof(struct __sk_buff, data_end)),
BPF_MOV64_REG(BPF_REG_0, BPF_REG_2),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 8),
BPF_JMP_REG(BPF_JGT, BPF_REG_0, BPF_REG_3, 4),
BPF_MOV64_REG(BPF_REG_1, BPF_REG_2),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, 6),
BPF_JMP_REG(BPF_JGT, BPF_REG_1, BPF_REG_3, 1),
BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_2, 6),
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
},
.result = ACCEPT,
.prog_type = BPF_PROG_TYPE_LWT_XMIT,
},
{ {
"invalid access of tc_classid for LWT_IN", "invalid access of tc_classid for LWT_IN",
.insns = { .insns = {