net: filter: make JITs zero A for SKF_AD_ALU_XOR_X

The SKF_AD_ALU_XOR_X ancillary is not like the other ancillary data
instructions since it XORs A with X while all the others replace A with
some loaded value.  All the BPF JITs fail to clear A if this is used as
the first instruction in a filter.  This was found using american fuzzy
lop.

Add a helper to determine if A needs to be cleared given the first
instruction in a filter, and use this in the JITs.  Except for ARM, the
rest have only been compile-tested.

Fixes: 3480593131e0 ("net: filter: get rid of BPF_S_* enum")
Signed-off-by: Rabin Vincent <rabin@rab.in>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 15 deletions

diff --git a/arch/sparc/net/bpf_jit_comp.c b/arch/sparc/net/bpf_jit_comp.c
index 22564f5f2364..3e6e05a7c4c2 100644
--- a/arch/sparc/net/bpf_jit_comp.c
+++ b/arch/sparc/net/bpf_jit_comp.c
@@ -420,22 +420,9 @@ void bpf_jit_compile(struct bpf_prog *fp)
                 }
                 emit_reg_move(O7, r_saved_O7);
 
-                switch (filter[0].code) {
-                case BPF_RET | BPF_K:
-                case BPF_LD | BPF_W | BPF_LEN:
-                case BPF_LD | BPF_W | BPF_ABS:
-                case BPF_LD | BPF_H | BPF_ABS:
-                case BPF_LD | BPF_B | BPF_ABS:
-                        /* The first instruction sets the A register (or is
-                         * a "RET 'constant'")
-                         */
-                        break;
-                default:
-                        /* Make sure we dont leak kernel information to the
-                         * user.
-                         */
+                /* Make sure we dont leak kernel information to the user. */
+                if (bpf_needs_clear_a(&filter[0]))
                         emit_clear(r_A); /* A = 0 */
-                }
 
                 for (i = 0; i < flen; i++) {
                         unsigned int K = filter[i].k;