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 <rabin@rab.in>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 15 insertions, 0 deletions

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a7945d10b378..d1d3e8f57de9 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 672eefbfbe99..37157c4c1a78 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: