netdev - [PATCH bpf-next v3] bpf: reject kfunc calls that overflow insn->imm

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Date:   Wed, 9 Feb 2022 17:11:53 +0800
From:   Hou Tao <houtao1@...wei.com>
To:     Alexei Starovoitov <ast@...nel.org>
CC:     Martin KaFai Lau <kafai@...com>, Yonghong Song <yhs@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <houtao1@...wei.com>
Subject: [PATCH bpf-next v3] bpf: reject kfunc calls that overflow insn->imm

Now kfunc call uses s32 to represent the offset between the address
of kfunc and __bpf_call_base, but it doesn't check whether or not
s32 will be overflowed, so add an extra checking to reject these
invalid kfunc calls.

Signed-off-by: Hou Tao <houtao1@...wei.com>
---
v3:
 * call BPF_CALL_IMM() once (suggested by Yonghong)

v2: https://lore.kernel.org/bpf/20220208123348.40360-1-houtao1@huawei.com
 * instead of checking the overflow in selftests, just reject
   these kfunc calls directly in verifier

v1: https://lore.kernel.org/bpf/20220206043107.18549-1-houtao1@huawei.com
---
 kernel/bpf/verifier.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1ae41d0cf96c..eb72e6139e2b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1842,6 +1842,7 @@ static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, s16 offset)
 	struct bpf_kfunc_desc *desc;
 	const char *func_name;
 	struct btf *desc_btf;
+	unsigned long call_imm;
 	unsigned long addr;
 	int err;
 
@@ -1926,9 +1927,17 @@ static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, s16 offset)
 		return -EINVAL;
 	}
 
+	call_imm = BPF_CALL_IMM(addr);
+	/* Check whether or not the relative offset overflows desc->imm */
+	if ((unsigned long)(s32)call_imm != call_imm) {
+		verbose(env, "address of kernel function %s is out of range\n",
+			func_name);
+		return -EINVAL;
+	}
+
 	desc = &tab->descs[tab->nr_descs++];
 	desc->func_id = func_id;
-	desc->imm = BPF_CALL_IMM(addr);
+	desc->imm = call_imm;
 	desc->offset = offset;
 	err = btf_distill_func_proto(&env->log, desc_btf,
 				     func_proto, func_name,
-- 
2.27.0