bpf: fix replace_map_fd_with_map_ptr's ldimm64 second imm field

Non-zero imm value in the second part of the ldimm64 instruction for
BPF_PSEUDO_MAP_FD is invalid, and thus must be rejected. The map fd
only ever sits in the first instructions' imm field. None of the BPF
loaders known to us are using it, so risk of regression is minimal.
For clarity and consistency, the few insn->{src_reg,imm} occurrences
are rewritten into insn[0].{src_reg,imm}. Add a test case to the BPF
selftest suite as well.

Fixes: 0246e64d ("bpf: handle pseudo BPF_LD_IMM64 insn")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/verifier.c

@@ -6678,17 +6678,17 @@ static int replace_map_fd_with_map_ptr(struct bpf_verifier_env *env)
 				/* valid generic load 64-bit imm */
 				goto next_insn;
 
-			if (insn->src_reg != BPF_PSEUDO_MAP_FD) {
-				verbose(env,
-					"unrecognized bpf_ld_imm64 insn\n");
+			if (insn[0].src_reg != BPF_PSEUDO_MAP_FD ||
+			    insn[1].imm != 0) {
+				verbose(env, "unrecognized bpf_ld_imm64 insn\n");
 				return -EINVAL;
 			}
 
-			f = fdget(insn->imm);
+			f = fdget(insn[0].imm);
 			map = __bpf_map_get(f);
 			if (IS_ERR(map)) {
 				verbose(env, "fd %d is not pointing to valid bpf_map\n",
-					insn->imm);
+					insn[0].imm);
 				return PTR_ERR(map);
 			}
 

tools/testing/selftests/bpf/verifier/ld_imm64.c

@@ -122,7 +122,7 @@
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_1, 0),
 	BPF_RAW_INSN(BPF_LD | BPF_IMM | BPF_DW, 0, BPF_REG_1, 0, 1),
-	BPF_RAW_INSN(0, 0, 0, 0, 1),
+	BPF_RAW_INSN(0, 0, 0, 0, 0),
 	BPF_EXIT_INSN(),
 	},
 	.errstr = "not pointing to valid bpf_map",
@@ -139,3 +139,16 @@
 	.errstr = "invalid bpf_ld_imm64 insn",
 	.result = REJECT,
 },
+{
+	"test14 ld_imm64: reject 2nd imm != 0",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_RAW_INSN(BPF_LD | BPF_IMM | BPF_DW, BPF_REG_1,
+		     BPF_PSEUDO_MAP_FD, 0, 0),
+	BPF_RAW_INSN(0, 0, 0, 0, 0xfefefe),
+	BPF_EXIT_INSN(),
+	},
+	.fixup_map_hash_48b = { 1 },
+	.errstr = "unrecognized bpf_ld_imm64 insn",
+	.result = REJECT,
+},