net: bpf_jit: fix BPF_S_LDX_B_MSH compilation

Matt Evans spotted that x86 bpf_jit was incorrectly handling negative
constant offsets in BPF_S_LDX_B_MSH instruction.

We need to abort JIT compilation like we do in common_load so that
filter uses the interpreter code and can call __load_pointer()

Reference: http://lists.openwall.net/netdev/2011/07/19/11

Thanks to Indan Zupancic to bring back this issue.

Reported-by: Matt Evans <matt@ozlabs.org>
Reported-by: Indan Zupancic <indan@nul.nu>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 9 deletions

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 7c1b765ecc59..5671752f8d9c 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -475,8 +475,10 @@ void bpf_jit_compile(struct sk_filter *fp)
                         case BPF_S_LD_W_ABS:
                                 func = sk_load_word;
 common_load:                    seen |= SEEN_DATAREF;
-                                if ((int)K < 0)
+                                if ((int)K < 0) {
+                                        /* Abort the JIT because __load_pointer() is needed. */
                                         goto out;
+                                }
                                 t_offset = func - (image + addrs[i]);
                                 EMIT1_off32(0xbe, K); /* mov imm32,%esi */
                                 EMIT1_off32(0xe8, t_offset); /* call */
@@ -489,14 +491,8 @@ common_load:			seen |= SEEN_DATAREF;
                                 goto common_load;
                         case BPF_S_LDX_B_MSH:
                                 if ((int)K < 0) {
-                                        if (pc_ret0 > 0) {
-                                                /* addrs[pc_ret0 - 1] is the start address */
-                                                EMIT_JMP(addrs[pc_ret0 - 1] - addrs[i]);
-                                                break;
-                                        }
-                                        CLEAR_A();
-                                        EMIT_JMP(cleanup_addr - addrs[i]);
-                                        break;
+                                        /* Abort the JIT because __load_pointer() is needed. */
+                                        goto out;
                                 }
                                 seen |= SEEN_DATAREF | SEEN_XREG;
                                 t_offset = sk_load_byte_msh - (image + addrs[i]);