bpf: enforce return code for cgroup-bpf programs

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>

2 files changed, 112 insertions, 0 deletions

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 4cf9b72c59a0..52b022310f6a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -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) {
diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 290d5056c165..cc91d0159f43 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -6892,6 +6892,78 @@ static struct bpf_test tests[] = {
                 .result = ACCEPT,
                 .prog_type = BPF_PROG_TYPE_XDP,
         },
+        {
+                "bpf_exit with invalid return code. test1",
+                .insns = {
+                        BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1, 0),
+                        BPF_EXIT_INSN(),
+                },
+                .errstr = "R0 has value (0x0; 0xffffffff)",
+                .result = REJECT,
+                .prog_type = BPF_PROG_TYPE_CGROUP_SOCK,
+        },
+        {
+                "bpf_exit with invalid return code. test2",
+                .insns = {
+                        BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1, 0),
+                        BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 1),
+                        BPF_EXIT_INSN(),
+                },
+                .result = ACCEPT,
+                .prog_type = BPF_PROG_TYPE_CGROUP_SOCK,
+        },
+        {
+                "bpf_exit with invalid return code. test3",
+                .insns = {
+                        BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1, 0),
+                        BPF_ALU64_IMM(BPF_AND, BPF_REG_0, 3),
+                        BPF_EXIT_INSN(),
+                },
+                .errstr = "R0 has value (0x0; 0x3)",
+                .result = REJECT,
+                .prog_type = BPF_PROG_TYPE_CGROUP_SOCK,
+        },
+        {
+                "bpf_exit with invalid return code. test4",
+                .insns = {
+                        BPF_MOV64_IMM(BPF_REG_0, 1),
+                        BPF_EXIT_INSN(),
+                },
+                .result = ACCEPT,
+                .prog_type = BPF_PROG_TYPE_CGROUP_SOCK,
+        },
+        {
+                "bpf_exit with invalid return code. test5",
+                .insns = {
+                        BPF_MOV64_IMM(BPF_REG_0, 2),
+                        BPF_EXIT_INSN(),
+                },
+                .errstr = "R0 has value (0x2; 0x0)",
+                .result = REJECT,
+                .prog_type = BPF_PROG_TYPE_CGROUP_SOCK,
+        },
+        {
+                "bpf_exit with invalid return code. test6",
+                .insns = {
+                        BPF_MOV64_REG(BPF_REG_0, BPF_REG_1),
+                        BPF_EXIT_INSN(),
+                },
+                .errstr = "R0 is not a known value (ctx)",
+                .result = REJECT,
+                .prog_type = BPF_PROG_TYPE_CGROUP_SOCK,
+        },
+        {
+                "bpf_exit with invalid return code. test7",
+                .insns = {
+                        BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1, 0),
+                        BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 4),
+                        BPF_ALU64_REG(BPF_MUL, BPF_REG_0, BPF_REG_2),
+                        BPF_EXIT_INSN(),
+                },
+                .errstr = "R0 has unknown scalar value",
+                .result = REJECT,
+                .prog_type = BPF_PROG_TYPE_CGROUP_SOCK,
+        },
 };
 
 static int probe_filter_length(const struct bpf_insn *fp)