Syzkaller reports the following crash:
RIP: 0010:check_return_code kernel/bpf/verifier.c:10575 [inline]
RIP: 0010:do_check kernel/bpf/verifier.c:12346 [inline]
RIP: 0010:do_check_common+0xb3d2/0xd250 kernel/bpf/verifier.c:14610
With the following reproducer:
bpf$PROG_LOAD_XDP(0x5, &(0x7f00000004c0)={0xd, 0x3, &(0x7f0000000000)=ANY=[@ANYBLOB="1800000000000019000000000000000095"], &(0x7f0000000300)='GPL\x00', 0x0, 0x0, 0x0, 0x0, 0x0, '\x00', 0x0, 0x2b, 0xffffffffffffffff, 0x8, 0x0, 0x0, 0x10, 0x0}, 0x80)
Because we don't enforce expected_attach_type for XDP programs,
we end up in hitting 'if (prog->expected_attach_type == BPF_LSM_CGROUP'
part in check_return_code and follow up with testing
`prog->aux->attach_func_proto->type`, but `prog->aux->attach_func_proto`
is NULL.
Let's add a new btf_func_returns_void() wrapper which is more defensive
and use it in the places where we currently do '!->type' check.
Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
Reported-by: syzbot+5cc0730bd4b4d2c5f152@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
---
include/linux/btf.h | 5 +++++
kernel/bpf/trampoline.c | 2 +-
kernel/bpf/verifier.c | 8 ++++----
3 files changed, 10 insertions(+), 5 deletions(-)
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 1bfed7fa0428..17ba7d27a8ad 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -302,6 +302,11 @@ static inline u16 btf_func_linkage(const struct btf_type *t)
return BTF_INFO_VLEN(t->info);
}
+static inline bool btf_func_returns_void(const struct btf_type *t)
+{
+ return t && !t->type;
+}
+
static inline bool btf_type_kflag(const struct btf_type *t)
{
return BTF_INFO_KFLAG(t->info);
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 6cd226584c33..9c4cb4c8a5fa 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -400,7 +400,7 @@ static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
case BPF_TRACE_FEXIT:
return BPF_TRAMP_FEXIT;
case BPF_LSM_MAC:
- if (!prog->aux->attach_func_proto->type)
+ if (btf_func_returns_void(prog->aux->attach_func_proto))
/* The function returns void, we cannot modify its
* return value.
*/
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index df3ec6b05f05..e3ee6f70939b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7325,7 +7325,7 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
break;
case BPF_FUNC_set_retval:
if (env->prog->expected_attach_type == BPF_LSM_CGROUP) {
- if (!env->prog->aux->attach_func_proto->type) {
+ if (btf_func_returns_void(env->prog->aux->attach_func_proto)) {
/* Make sure programs that attach to void
* hooks don't try to modify return value.
*/
@@ -10447,7 +10447,7 @@ static int check_return_code(struct bpf_verifier_env *env)
if (!is_subprog &&
(prog_type == BPF_PROG_TYPE_STRUCT_OPS ||
prog_type == BPF_PROG_TYPE_LSM) &&
- !prog->aux->attach_func_proto->type)
+ btf_func_returns_void(prog->aux->attach_func_proto))
return 0;
/* eBPF calling convention is such that R0 is used
@@ -10547,7 +10547,7 @@ static int check_return_code(struct bpf_verifier_env *env)
*/
return 0;
}
- if (!env->prog->aux->attach_func_proto->type) {
+ if (btf_func_returns_void(env->prog->aux->attach_func_proto)) {
/* Make sure programs that attach to void
* hooks don't try to modify return value.
*/
@@ -10572,7 +10572,7 @@ static int check_return_code(struct bpf_verifier_env *env)
if (!tnum_in(range, reg->var_off)) {
verbose_invalid_scalar(env, reg, &range, "program exit", "R0");
if (prog->expected_attach_type == BPF_LSM_CGROUP &&
- !prog->aux->attach_func_proto->type)
+ btf_func_returns_void(prog->aux->attach_func_proto))
verbose(env, "Note, BPF_LSM_CGROUP that attach to void LSM hooks can't modify return value!\n");
return -EINVAL;
}
--
2.37.0.rc0.161.g10f37bed90-goog
