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bpf: enforce return code for cgroup-bpf programs

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with addition of tnum logic the verifier got smart enough and
we can enforce return codes at program load time.
For now do so for cgroup-bpf program types.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov
2017-10-02 22:50:23 -07:00
committed by David S. Miller
parent 468e2f64d2
commit 390ee7e29f
2 changed files with 112 additions and 0 deletions
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40
kernel/bpf/verifier.c
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@@ -3073,6 +3073,43 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn)
return 0;
}
static int check_return_code(struct bpf_verifier_env *env)
{
struct bpf_reg_state *reg;
struct tnum range = tnum_range(0, 1);
switch (env->prog->type) {
case BPF_PROG_TYPE_CGROUP_SKB:
case BPF_PROG_TYPE_CGROUP_SOCK:
case BPF_PROG_TYPE_SOCK_OPS:
break;
default:
return 0;
}
reg = &env->cur_state.regs[BPF_REG_0];
if (reg->type != SCALAR_VALUE) {
verbose("At program exit the register R0 is not a known value (%s)\n",
reg_type_str[reg->type]);
return -EINVAL;
}
if (!tnum_in(range, reg->var_off)) {
verbose("At program exit the register R0 ");
if (!tnum_is_unknown(reg->var_off)) {
char tn_buf[48];
tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off);
verbose("has value %s", tn_buf);
} else {
verbose("has unknown scalar value");
}
verbose(" should have been 0 or 1\n");
return -EINVAL;
}
return 0;
}
/* non-recursive DFS pseudo code
* 1 procedure DFS-iterative(G,v):
* 2 label v as discovered
@@ -3863,6 +3900,9 @@ static int do_check(struct bpf_verifier_env *env)
return -EACCES;
}
err = check_return_code(env);
if (err)
return err;
process_bpf_exit:
insn_idx = pop_stack(env, &prev_insn_idx);
if (insn_idx < 0) {