[PATCH v2 bpf-next 12/17] bpf: Fix race in btf_resolve_helper_id()
From: Alexei Starovoitov <ast@kernel.org>
Date: 2019-11-07 05:47:35
Also in:
bpf
Subsystem:
bpf [core], bpf [general] (safe dynamic programs and tools), the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds
btf_resolve_helper_id() caching logic is racy, since under root the verifier
can verify several programs in parallel. Fix it with extra spin_lock.
Fixes: a7658e1a4164 ("bpf: Check types of arguments passed into helpers")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
include/linux/bpf.h | 3 ++-
kernel/bpf/btf.c | 34 +++++++++++++++++++++++++++++++++-
kernel/bpf/verifier.c | 6 +-----
3 files changed, 36 insertions(+), 7 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 9206b7e86dde..c287dfce2a17 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h@@ -874,7 +874,8 @@ int btf_struct_access(struct bpf_verifier_log *log, const struct btf_type *t, int off, int size, enum bpf_access_type atype, u32 *next_btf_id); -u32 btf_resolve_helper_id(struct bpf_verifier_log *log, void *, int); +u32 btf_resolve_helper_id(struct bpf_verifier_log *log, + const struct bpf_func_proto *fn, int); int btf_distill_func_proto(struct bpf_verifier_log *log, struct btf *btf,
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 78d9ceaabc00..7155787a0b13 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c@@ -3584,7 +3584,8 @@ int btf_struct_access(struct bpf_verifier_log *log, return -EINVAL; } -u32 btf_resolve_helper_id(struct bpf_verifier_log *log, void *fn, int arg) +static u32 __btf_resolve_helper_id(struct bpf_verifier_log *log, void *fn, + int arg) { char fnname[KSYM_SYMBOL_LEN + 4] = "btf_"; const struct btf_param *args;
@@ -3652,6 +3653,37 @@ u32 btf_resolve_helper_id(struct bpf_verifier_log *log, void *fn, int arg) return btf_id; } +static DEFINE_SPINLOCK(btf_resolve_lock); + +u32 btf_resolve_helper_id(struct bpf_verifier_log *log, + const struct bpf_func_proto *fn, int arg) +{ + u32 *btf_id = &fn->btf_id[arg]; + u32 ret; + + if (fn->arg_type[arg] != ARG_PTR_TO_BTF_ID) + return -EINVAL; + + if (*btf_id) + /* ok to do without lock. It only set once */ + return *btf_id; + /* ok to race the search. The result is the same */ + ret = __btf_resolve_helper_id(log, fn->func, arg); + if (!ret) { + bpf_log(log, "BTF resolution bug\n"); + return -EFAULT; + } + spin_lock(&btf_resolve_lock); + if (*btf_id) { + ret = *btf_id; + goto out; + } + *btf_id = ret; +out: + spin_unlock(&btf_resolve_lock); + return ret; +} + static int __get_type_size(struct btf *btf, u32 btf_id, const struct btf_type **bad_type) {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 36542edd4936..c4fd11a27d81 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c@@ -4147,11 +4147,7 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn meta.func_id = func_id; /* check args */ for (i = 0; i < 5; i++) { - if (fn->arg_type[i] == ARG_PTR_TO_BTF_ID) { - if (!fn->btf_id[i]) - fn->btf_id[i] = btf_resolve_helper_id(&env->log, fn->func, i); - meta.btf_id = fn->btf_id[i]; - } + meta.btf_id = btf_resolve_helper_id(&env->log, fn, i); err = check_func_arg(env, BPF_REG_1 + i, fn->arg_type[i], &meta); if (err) return err;
--
2.23.0