filter: add MOD operation

Add a new ALU opcode, to compute a modulus.

Commit ffe06c17afbbb used an ancillary to implement XOR_X,
but here we reserve one of the available ALU opcode to implement both
MOD_X and MOD_K

Signed-off-by: Eric Dumazet <edumazet@google.com>
Suggested-by: George Bakos <gbakos@alpinista.org>
Cc: Jay Schulist <jschlst@samba.org>
Cc: Jiri Pirko <jpirko@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 15 insertions, 0 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index 907efd27ec77..fbe3a8d12570 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -167,6 +167,14 @@ unsigned int sk_run_filter(const struct sk_buff *skb,
                 case BPF_S_ALU_DIV_K:
                         A = reciprocal_divide(A, K);
                         continue;
+                case BPF_S_ALU_MOD_X:
+                        if (X == 0)
+                                return 0;
+                        A %= X;
+                        continue;
+                case BPF_S_ALU_MOD_K:
+                        A %= K;
+                        continue;
                 case BPF_S_ALU_AND_X:
                         A &= X;
                         continue;
@@ -469,6 +477,8 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
                 [BPF_ALU|BPF_MUL|BPF_K]  = BPF_S_ALU_MUL_K,
                 [BPF_ALU|BPF_MUL|BPF_X]  = BPF_S_ALU_MUL_X,
                 [BPF_ALU|BPF_DIV|BPF_X]  = BPF_S_ALU_DIV_X,
+                [BPF_ALU|BPF_MOD|BPF_K]  = BPF_S_ALU_MOD_K,
+                [BPF_ALU|BPF_MOD|BPF_X]  = BPF_S_ALU_MOD_X,
                 [BPF_ALU|BPF_AND|BPF_K]  = BPF_S_ALU_AND_K,
                 [BPF_ALU|BPF_AND|BPF_X]  = BPF_S_ALU_AND_X,
                 [BPF_ALU|BPF_OR|BPF_K]   = BPF_S_ALU_OR_K,
@@ -531,6 +541,11 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
                                 return -EINVAL;
                         ftest->k = reciprocal_value(ftest->k);
                         break;
+                case BPF_S_ALU_MOD_K:
+                        /* check for division by zero */
+                        if (ftest->k == 0)
+                                return -EINVAL;
+                        break;
                 case BPF_S_LD_MEM:
                 case BPF_S_LDX_MEM:
                 case BPF_S_ST: