netdev - [PATCH 4.4-stable 4/6] bpf: refactor fixup_bpf

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Date:   Fri, 12 Jan 2018 17:17:19 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     gregkh@...uxfoundation.org
Cc:     stable@...r.kernel.org, ast@...nel.org, netdev@...r.kernel.org,
        Alexei Starovoitov <ast@...com>,
        "David S . Miller" <davem@...emloft.net>,
        Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 4.4-stable 4/6] bpf: refactor fixup_bpf_calls()

From: Alexei Starovoitov <ast@...com>

commit 79741b3bdec01a8628368fbcfccc7d189ed606cb upstream.

reduce indent and make it iterate over instructions similar to
convert_ctx_accesses(). Also convert hard BUG_ON into soft verifier error.

Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Acked-by: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 kernel/bpf/verifier.c | 72 +++++++++++++++++++++++----------------------------
 1 file changed, 33 insertions(+), 39 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 198737d36754..47bb3eee950c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2158,57 +2158,51 @@ static int convert_ctx_accesses(struct verifier_env *env)
 	return 0;
 }
 
-/* fixup insn->imm field of bpf_call instructions:
- * if (insn->imm == BPF_FUNC_map_lookup_elem)
- *      insn->imm = bpf_map_lookup_elem - __bpf_call_base;
- * else if (insn->imm == BPF_FUNC_map_update_elem)
- *      insn->imm = bpf_map_update_elem - __bpf_call_base;
- * else ...
+/* fixup insn->imm field of bpf_call instructions
  *
  * this function is called after eBPF program passed verification
  */
-static void fixup_bpf_calls(struct bpf_prog *prog)
+static int fixup_bpf_calls(struct verifier_env *env)
 {
+	struct bpf_prog *prog = env->prog;
+	struct bpf_insn *insn = prog->insnsi;
 	const struct bpf_func_proto *fn;
+	const int insn_cnt = prog->len;
 	int i;
 
-	for (i = 0; i < prog->len; i++) {
-		struct bpf_insn *insn = &prog->insnsi[i];
+	for (i = 0; i < insn_cnt; i++, insn++) {
+		if (insn->code != (BPF_JMP | BPF_CALL))
+			continue;
 
-		if (insn->code == (BPF_JMP | BPF_CALL)) {
-			/* we reach here when program has bpf_call instructions
-			 * and it passed bpf_check(), means that
-			 * ops->get_func_proto must have been supplied, check it
+		if (insn->imm == BPF_FUNC_get_route_realm)
+			prog->dst_needed = 1;
+		if (insn->imm == BPF_FUNC_get_prandom_u32)
+			bpf_user_rnd_init_once();
+		if (insn->imm == BPF_FUNC_tail_call) {
+			/* mark bpf_tail_call as different opcode to avoid
+			 * conditional branch in the interpeter for every normal
+			 * call and to prevent accidental JITing by JIT compiler
+			 * that doesn't support bpf_tail_call yet
 			 */
-			BUG_ON(!prog->aux->ops->get_func_proto);
-
-			if (insn->imm == BPF_FUNC_get_route_realm)
-				prog->dst_needed = 1;
-			if (insn->imm == BPF_FUNC_get_prandom_u32)
-				bpf_user_rnd_init_once();
-			if (insn->imm == BPF_FUNC_tail_call) {
-				/* mark bpf_tail_call as different opcode
-				 * to avoid conditional branch in
-				 * interpeter for every normal call
-				 * and to prevent accidental JITing by
-				 * JIT compiler that doesn't support
-				 * bpf_tail_call yet
-				 */
-				insn->imm = 0;
-				insn->code |= BPF_X;
-				continue;
-			}
+			insn->imm = 0;
+			insn->code |= BPF_X;
+			continue;
+		}
 
-			fn = prog->aux->ops->get_func_proto(insn->imm);
-			/* all functions that have prototype and verifier allowed
-			 * programs to call them, must be real in-kernel functions
-			 */
-			BUG_ON(!fn->func);
-			insn->imm = fn->func - __bpf_call_base;
+		fn = prog->aux->ops->get_func_proto(insn->imm);
+		/* all functions that have prototype and verifier allowed
+		 * programs to call them, must be real in-kernel functions
+		 */
+		if (!fn->func) {
+			verbose("kernel subsystem misconfigured func %d\n",
+				insn->imm);
+			return -EFAULT;
 		}
+		insn->imm = fn->func - __bpf_call_base;
 	}
-}
 
+	return 0;
+}
 
 static void free_states(struct verifier_env *env)
 {
@@ -2309,7 +2303,7 @@ skip_full_check:
 		ret = convert_ctx_accesses(env);
 
 	if (ret == 0)
-		fixup_bpf_calls(env->prog);
+		ret = fixup_bpf_calls(env);
 
 	if (log_level && log_len >= log_size - 1) {
 		BUG_ON(log_len >= log_size);
-- 
2.15.1