net: bpf: reject invalid shifts

On ARM64, a BUG() is triggered in the eBPF JIT if a filter with a constant shift that can't be encoded in the immediate field of the UBFM/SBFM instructions is passed to the JIT. Since these shifts amounts, which are negative or >= regsize, are invalid, reject them in the eBPF verifier and the classic BPF filter checker, for all architectures. Signed-off-by: Rabin Vincent <[email protected]> Acked-by: Alexei Starovoitov <[email protected]> Acked-by: Daniel Borkmann <[email protected]> Signed-off-by: David S. Miller <[email protected]>
mrcsosa · Jan 12, 2016 · 06928b3 · 06928b3
1 parent 03d84a5
commit 06928b3
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diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
@@ -1121,6 +1121,16 @@ static int check_alu_op(struct verifier_env *env, struct bpf_insn *insn)
 			return -EINVAL;
 		}
 
+		if ((opcode == BPF_LSH || opcode == BPF_RSH ||
+		     opcode == BPF_ARSH) && BPF_SRC(insn->code) == BPF_K) {
+			int size = BPF_CLASS(insn->code) == BPF_ALU64 ? 64 : 32;
+
+			if (insn->imm < 0 || insn->imm >= size) {
+				verbose("invalid shift %d\n", insn->imm);
+				return -EINVAL;
+			}
+		}
+
 		/* pattern match 'bpf_add Rx, imm' instruction */
 		if (opcode == BPF_ADD && BPF_CLASS(insn->code) == BPF_ALU64 &&
 		    regs[insn->dst_reg].type == FRAME_PTR &&

diff --git a/net/core/filter.c b/net/core/filter.c
@@ -777,6 +777,11 @@ static int bpf_check_classic(const struct sock_filter *filter,
 			if (ftest->k == 0)
 				return -EINVAL;
 			break;
+		case BPF_ALU | BPF_LSH | BPF_K:
+		case BPF_ALU | BPF_RSH | BPF_K:
+			if (ftest->k >= 32)
+				return -EINVAL;
+			break;
 		case BPF_LD | BPF_MEM:
 		case BPF_LDX | BPF_MEM:
 		case BPF_ST: