[PATCH bpf-next 3/4] bpf: Allow local storage to be used from LSM programs

[KP Singh]

From: KP Singh <kpsingh at google.com>

Adds support for both bpf_{sk, inode}_storage_{get, delete} to be used
in LSM programs. These helpers are not used for tracing programs
(currently) as their usage is tied to the life-cycle of the object and
should only be used where the owning object won't be freed. Thus, they
are safe to use in LSM hooks, but can only be enabled in tracing
programs using a whitelist based approach.

Since the UAPI helper signature for bpf_sk_storage expect a bpf_sock,
it, leads to a compilation warning for LSM programs, it's also updated
to accept a void * pointer instead.

Signed-off-by: KP Singh <kpsingh at google.com>
---
 include/linux/bpf_local_storage.h |  2 ++
 kernel/bpf/bpf_local_storage.c    | 22 ++++++++++++++++++++++
 kernel/bpf/bpf_lsm.c              | 20 +++++++++++++++++++-
 3 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/include/linux/bpf_local_storage.h b/include/linux/bpf_local_storage.h
index c6837e7838fc..8982c0c69332 100644
--- a/include/linux/bpf_local_storage.h
+++ b/include/linux/bpf_local_storage.h
@@ -9,6 +9,8 @@ void bpf_sk_storage_free(struct sock *sk);
 
 extern const struct bpf_func_proto bpf_sk_storage_get_proto;
 extern const struct bpf_func_proto bpf_sk_storage_delete_proto;
+extern const struct bpf_func_proto sk_storage_get_btf_proto;
+extern const struct bpf_func_proto sk_storage_delete_btf_proto;
 extern const struct bpf_func_proto bpf_inode_storage_get_proto;
 extern const struct bpf_func_proto bpf_inode_storage_delete_proto;
 
diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
index bf807cfe3a73..07e02d32feb0 100644
--- a/kernel/bpf/bpf_local_storage.c
+++ b/kernel/bpf/bpf_local_storage.c
@@ -1305,6 +1305,28 @@ const struct bpf_func_proto bpf_inode_storage_delete_proto = {
 	.btf_id		= bpf_inode_storage_delete_btf_ids,
 };
 
+static int sk_storage_get_btf_ids[4];
+const struct bpf_func_proto sk_storage_get_btf_proto = {
+	.func		= bpf_sk_storage_get,
+	.gpl_only	= false,
+	.ret_type	= RET_PTR_TO_MAP_VALUE_OR_NULL,
+	.arg1_type	= ARG_CONST_MAP_PTR,
+	.arg2_type	= ARG_PTR_TO_BTF_ID,
+	.arg3_type	= ARG_PTR_TO_MAP_VALUE_OR_NULL,
+	.arg4_type	= ARG_ANYTHING,
+	.btf_id		= sk_storage_get_btf_ids,
+};
+
+static int sk_storage_delete_btf_ids[2];
+const struct bpf_func_proto sk_storage_delete_btf_proto = {
+	.func		= bpf_sk_storage_delete,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_CONST_MAP_PTR,
+	.arg2_type	= ARG_PTR_TO_BTF_ID,
+	.btf_id		= sk_storage_delete_btf_ids,
+};
+
 struct bpf_sk_storage_diag {
 	u32 nr_maps;
 	struct bpf_map *maps[];
diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index 19636703b24e..fce0a11b63ca 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -11,6 +11,7 @@
 #include <linux/bpf_lsm.h>
 #include <linux/kallsyms.h>
 #include <linux/bpf_verifier.h>
+#include <linux/bpf_local_storage.h>
 
 /* For every LSM hook that allows attachment of BPF programs, declare a nop
  * function where a BPF program can be attached.
@@ -45,10 +46,27 @@ int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
 	return 0;
 }
 
+static const struct bpf_func_proto *
+bpf_lsm_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
+{
+	switch (func_id) {
+	case BPF_FUNC_inode_storage_get:
+		return &bpf_inode_storage_get_proto;
+	case BPF_FUNC_inode_storage_delete:
+		return &bpf_inode_storage_delete_proto;
+	case BPF_FUNC_sk_storage_get:
+		return &sk_storage_get_btf_proto;
+	case BPF_FUNC_sk_storage_delete:
+		return &sk_storage_delete_btf_proto;
+	default:
+		return bpf_tracing_func_proto(func_id, prog);
+	}
+}
+
 const struct bpf_prog_ops lsm_prog_ops = {
 };
 
 const struct bpf_verifier_ops lsm_verifier_ops = {
-	.get_func_proto = bpf_tracing_func_proto,
+	.get_func_proto = bpf_lsm_func_proto,
 	.is_valid_access = btf_ctx_access,
 };
-- 
2.27.0.rc0.183.gde8f92d652-goog