linux-kernel - [PATCH 5.11 111/254] bpf: Dont allow vmlinux BTF to be used in map_create and prog

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Date:   Mon, 29 Mar 2021 09:57:07 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+8bab8ed346746e7540e8@...kaller.appspotmail.com,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yonghong Song <yhs@...com>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.11 111/254] bpf: Dont allow vmlinux BTF to be used in map_create and prog_load.

From: Alexei Starovoitov <ast@...nel.org>

[ Upstream commit 350a5c4dd2452ea999cc5e1d4a8dbf12de2f97ef ]

The syzbot got FD of vmlinux BTF and passed it into map_create which caused
crash in btf_type_id_size() when it tried to access resolved_ids. The vmlinux
BTF doesn't have 'resolved_ids' and 'resolved_sizes' initialized to save
memory. To avoid such issues disallow using vmlinux BTF in prog_load and
map_create commands.

Fixes: 5329722057d4 ("bpf: Assign ID to vmlinux BTF and return extra info for BTF in GET_OBJ_INFO")
Reported-by: syzbot+8bab8ed346746e7540e8@...kaller.appspotmail.com
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Yonghong Song <yhs@...com>
Link: https://lore.kernel.org/bpf/20210307225248.79031-1-alexei.starovoitov@gmail.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/bpf/syscall.c  | 5 +++++
 kernel/bpf/verifier.c | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e5999d86c76e..32ca33539052 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -854,6 +854,11 @@ static int map_create(union bpf_attr *attr)
 			err = PTR_ERR(btf);
 			goto free_map;
 		}
+		if (btf_is_kernel(btf)) {
+			btf_put(btf);
+			err = -EACCES;
+			goto free_map;
+		}
 		map->btf = btf;
 
 		if (attr->btf_value_type_id) {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ab23dfb9df1b..5b233e911c2c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8580,6 +8580,10 @@ static int check_btf_info(struct bpf_verifier_env *env,
 	btf = btf_get_by_fd(attr->prog_btf_fd);
 	if (IS_ERR(btf))
 		return PTR_ERR(btf);
+	if (btf_is_kernel(btf)) {
+		btf_put(btf);
+		return -EACCES;
+	}
 	env->prog->aux->btf = btf;
 
 	err = check_btf_func(env, attr, uattr);
-- 
2.30.1