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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 <[email protected]>
Fixes: 969bf05eb3 ("bpf: direct packet access")
Signed-off-by: Alexei Starovoitov <[email protected]>
Acked-by: Daniel Borkmann <[email protected]>
Acked-by: Martin KaFai Lau <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Alexei Starovoitov 2017-03-24 15:57:33 -07:00 • committed by David S. Miller
commit b1977682a3
2 changed files with 23 additions and 2 deletions
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5
kernel/bpf/verifier.c
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@ -1973,14 +1973,15 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *state,
for (i = 0; i < MAX_BPF_REG; i++)
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) {
if (state->stack_slot_type[i] != STACK_SPILL)
continue;
reg = &state->spilled_regs[i / BPF_REG_SIZE];
if (reg->type == PTR_TO_PACKET && reg->id == dst_reg->id)
reg->range = dst_reg->off;
reg->range = max(reg->range, dst_reg->off);
}
}