bpf: fix out of bounds access in verifier log

when the verifier log is enabled the print_bpf_insn() is doing
bpf_alu_string[BPF_OP(insn->code) >> 4]
and
bpf_jmp_string[BPF_OP(insn->code) >> 4]
where BPF_OP is a 4-bit instruction opcode.
Malformed insns can cause out of bounds access.
Fix it by sizing arrays appropriately.

The bug was found by clang address sanitizer with libfuzzer.

Reported-by: Yonghong Song <yhs@plumgrid.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ed12e38..b074b23 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -283,7 +283,7 @@ static const char *const bpf_class_string[] = {
        [BPF_ALU64] = "alu64",
 };
 
-static const char *const bpf_alu_string[] = {
+static const char *const bpf_alu_string[16] = {
        [BPF_ADD >> 4]  = "+=",
        [BPF_SUB >> 4]  = "-=",
        [BPF_MUL >> 4]  = "*=",
@@ -307,7 +307,7 @@ static const char *const bpf_ldst_string[] = {
        [BPF_DW >> 3] = "u64",
 };
 
-static const char *const bpf_jmp_string[] = {
+static const char *const bpf_jmp_string[16] = {
        [BPF_JA >> 4]   = "jmp",
        [BPF_JEQ >> 4]  = "==",
        [BPF_JGT >> 4]  = ">",