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Message-Id: <20220407223112.1204582-5-sdf@google.com>
Date: Thu, 7 Apr 2022 15:31:09 -0700
From: Stanislav Fomichev <sdf@...gle.com>
To: netdev@...r.kernel.org, bpf@...r.kernel.org
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
Stanislav Fomichev <sdf@...gle.com>
Subject: [PATCH bpf-next v3 4/7] bpf: allow writing to a subset of sock fields
from lsm progtype
For now, allow only the obvious ones, like sk_priority and sk_mark.
Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
---
kernel/bpf/bpf_lsm.c | 58 +++++++++++++++++++++++++++++++++++++++++++
kernel/bpf/verifier.c | 3 ++-
2 files changed, 60 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index 8b948ec9ab73..cc13da18d8b3 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -332,7 +332,65 @@ bool bpf_lsm_is_sleepable_hook(u32 btf_id)
const struct bpf_prog_ops lsm_prog_ops = {
};
+static int lsm_btf_struct_access(struct bpf_verifier_log *log,
+ const struct btf *btf,
+ const struct btf_type *t, int off,
+ int size, enum bpf_access_type atype,
+ u32 *next_btf_id,
+ enum bpf_type_flag *flag)
+{
+ const struct btf_type *sock_type;
+ struct btf *btf_vmlinux;
+ s32 type_id;
+ size_t end;
+
+ if (atype == BPF_READ)
+ return btf_struct_access(log, btf, t, off, size, atype, next_btf_id,
+ flag);
+
+ btf_vmlinux = bpf_get_btf_vmlinux();
+ if (!btf_vmlinux) {
+ bpf_log(log, "no vmlinux btf\n");
+ return -EOPNOTSUPP;
+ }
+
+ type_id = btf_find_by_name_kind(btf_vmlinux, "sock", BTF_KIND_STRUCT);
+ if (type_id < 0) {
+ bpf_log(log, "'struct sock' not found in vmlinux btf\n");
+ return -EINVAL;
+ }
+
+ sock_type = btf_type_by_id(btf_vmlinux, type_id);
+
+ if (t != sock_type) {
+ bpf_log(log, "only 'struct sock' writes are supported\n");
+ return -EACCES;
+ }
+
+ switch (off) {
+ case bpf_ctx_range(struct sock, sk_priority):
+ end = offsetofend(struct sock, sk_priority);
+ break;
+ case bpf_ctx_range(struct sock, sk_mark):
+ end = offsetofend(struct sock, sk_mark);
+ break;
+ default:
+ bpf_log(log, "no write support to 'struct sock' at off %d\n", off);
+ return -EACCES;
+ }
+
+ if (off + size > end) {
+ bpf_log(log,
+ "write access at off %d with size %d beyond the member of 'struct sock' ended at %zu\n",
+ off, size, end);
+ return -EACCES;
+ }
+
+ return NOT_INIT;
+}
+
const struct bpf_verifier_ops lsm_verifier_ops = {
.get_func_proto = bpf_lsm_func_proto,
.is_valid_access = btf_ctx_access,
+ .btf_struct_access = lsm_btf_struct_access,
};
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index cc84954846d7..0d6d5be30a36 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12872,7 +12872,8 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
insn->code = BPF_LDX | BPF_PROBE_MEM |
BPF_SIZE((insn)->code);
env->prog->aux->num_exentries++;
- } else if (resolve_prog_type(env->prog) != BPF_PROG_TYPE_STRUCT_OPS) {
+ } else if (resolve_prog_type(env->prog) != BPF_PROG_TYPE_STRUCT_OPS &&
+ resolve_prog_type(env->prog) != BPF_PROG_TYPE_LSM) {
verbose(env, "Writes through BTF pointers are not allowed\n");
return -EINVAL;
}
--
2.35.1.1178.g4f1659d476-goog
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