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bpf: cgroup inet skb programs can return 0 to 3 

Allows cgroup inet skb programs to return values in the range [0, 3].
The second bit is used to deterine if congestion occurred and higher
level protocol should decrease rate. E.g. TCP would call tcp_enter_cwr()

The bpf_prog must set expected_attach_type to BPF_CGROUP_INET_EGRESS
at load time if it uses the new return values (i.e. 2 or 3).

The expected_attach_type is currently not enforced for
BPF_PROG_TYPE_CGROUP_SKB.  e.g Meaning the current bpf_prog with
expected_attach_type setting to BPF_CGROUP_INET_EGRESS can attach to
BPF_CGROUP_INET_INGRESS.  Blindly enforcing expected_attach_type will
break backward compatibility.

This patch adds a enforce_expected_attach_type bit to only
enforce the expected_attach_type when it uses the new
return value.

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
brakmo 2019-05-28 16:59:36 -07:00 committed by Alexei Starovoitov
parent 1f52f6c0b0
commit 5cf1e91456
3 changed files with 27 additions and 4 deletions
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3
include/linux/filter.h
View File

@ -526,7 +526,8 @@ struct bpf_prog {
blinded:1, /* Was blinded */
is_func:1, /* program is a bpf function */
kprobe_override:1, /* Do we override a kprobe? */
has_callchain_buf:1; /* callchain buffer allocated? */
has_callchain_buf:1, /* callchain buffer allocated? */
enforce_expected_attach_type:1; /* Enforce expected_attach_type checking at attach time */
enum bpf_prog_type type; /* Type of BPF program */
enum bpf_attach_type expected_attach_type; /* For some prog types */
u32 len; /* Number of filter blocks */

12
kernel/bpf/syscall.c
View File

@ -1585,6 +1585,14 @@ bpf_prog_load_check_attach_type(enum bpf_prog_type prog_type,
default:
return -EINVAL;
}
case BPF_PROG_TYPE_CGROUP_SKB:
switch (expected_attach_type) {
case BPF_CGROUP_INET_INGRESS:
case BPF_CGROUP_INET_EGRESS:
return 0;
default:
return -EINVAL;
}
default:
return 0;
}
@ -1836,6 +1844,10 @@ static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog,
case BPF_PROG_TYPE_CGROUP_SOCK:
case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
return attach_type == prog->expected_attach_type ? 0 : -EINVAL;
case BPF_PROG_TYPE_CGROUP_SKB:
return prog->enforce_expected_attach_type &&
prog->expected_attach_type != attach_type ?
-EINVAL : 0;
default:
return 0;
}

16
kernel/bpf/verifier.c
View File

@ -5508,11 +5508,16 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn)
static int check_return_code(struct bpf_verifier_env *env)
{
struct tnum enforce_attach_type_range = tnum_unknown;
struct bpf_reg_state *reg;
struct tnum range = tnum_range(0, 1);
switch (env->prog->type) {
case BPF_PROG_TYPE_CGROUP_SKB:
if (env->prog->expected_attach_type == BPF_CGROUP_INET_EGRESS) {
range = tnum_range(0, 3);
enforce_attach_type_range = tnum_range(2, 3);
}
case BPF_PROG_TYPE_CGROUP_SOCK:
case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
case BPF_PROG_TYPE_SOCK_OPS:
@ -5531,18 +5536,23 @@ static int check_return_code(struct bpf_verifier_env *env)
}
if (!tnum_in(range, reg->var_off)) {
verbose(env, "At program exit the register R0 ");
if (!tnum_is_unknown(reg->var_off)) {
char tn_buf[48];
verbose(env, "At program exit the register R0 ");
if (!tnum_is_unknown(reg->var_off)) {
tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off);
verbose(env, "has value %s", tn_buf);
} else {
verbose(env, "has unknown scalar value");
}
verbose(env, " should have been 0 or 1\n");
tnum_strn(tn_buf, sizeof(tn_buf), range);
verbose(env, " should have been %s\n", tn_buf);
return -EINVAL;
}
if (!tnum_is_unknown(enforce_attach_type_range) &&
tnum_in(enforce_attach_type_range, reg->var_off))
env->prog->enforce_expected_attach_type = 1;
return 0;
}