Subject: [PATCH 13/24] net: bpf: reject invalid shifts

From: Rabin Vincent <[email-masked]>
Date: Tue, 12 Jan 2016 20:17:08 +0100

[ Upstream commit 229394e8e62a4191d592842cf67e80c62a492937 ]

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-masked]>
Acked-by: Alexei Starovoitov <[email-masked]>
Acked-by: Daniel Borkmann <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 kernel/bpf/verifier.c | 10 ++++++++++
 net/core/filter.c     |  5 +++++
 2 files changed, 15 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a7945d1..d1d3e8f 100644
--- 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
index 672eefb..37157c4 100644
--- 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:
-- 
2.1.0