6 files changed, 39 insertions, 2 deletions

diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
index 81f940f4e884..82e1cb0b3da8 100644
--- a/Documentation/networking/filter.txt
+++ b/Documentation/networking/filter.txt
@@ -281,6 +281,7 @@ Possible BPF extensions are shown in the following table:
   cpu                                   raw_smp_processor_id()
   vlan_tci                              vlan_tx_tag_get(skb)
   vlan_pr                               vlan_tx_tag_present(skb)
+  rand                                  prandom_u32()
 
 These extensions can also be prefixed with '#'.
 Examples for low-level BPF:
@@ -308,6 +309,18 @@ Examples for low-level BPF:
   ret #-1
   drop: ret #0
 
+** icmp random packet sampling, 1 in 4
+  ldh [12]
+  jne #0x800, drop
+  ldb [23]
+  jneq #1, drop
+  # get a random uint32 number
+  ld rand
+  mod #4
+  jneq #1, drop
+  ret #-1
+  drop: ret #0
+
 ** SECCOMP filter example:
 
   ld [4]                  /* offsetof(struct seccomp_data, arch) */
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 024fd03e5d18..759abf78dd61 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -223,6 +223,7 @@ enum {
         BPF_S_ANC_VLAN_TAG,
         BPF_S_ANC_VLAN_TAG_PRESENT,
         BPF_S_ANC_PAY_OFFSET,
+        BPF_S_ANC_RANDOM,
 };
 
 #endif /* __LINUX_FILTER_H__ */
diff --git a/include/uapi/linux/filter.h b/include/uapi/linux/filter.h
index 8eb9ccaa5b48..253b4d42cf2b 100644
--- a/include/uapi/linux/filter.h
+++ b/include/uapi/linux/filter.h
@@ -130,7 +130,8 @@ struct sock_fprog {	/* Required for SO_ATTACH_FILTER. */
 #define SKF_AD_VLAN_TAG 44
 #define SKF_AD_VLAN_TAG_PRESENT 48
 #define SKF_AD_PAY_OFFSET       52
-#define SKF_AD_MAX      56
+#define SKF_AD_RANDOM   56
+#define SKF_AD_MAX      60
 #define SKF_NET_OFF   (-0x100000)
 #define SKF_LL_OFF    (-0x200000)
 
diff --git a/net/core/filter.c b/net/core/filter.c
index cd58614660cf..78a636e60a0b 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -643,6 +643,12 @@ static u64 __get_raw_cpu_id(u64 ctx, u64 A, u64 X, u64 r4, u64 r5)
         return raw_smp_processor_id();
 }
 
+/* note that this only generates 32-bit random numbers */
+static u64 __get_random_u32(u64 ctx, u64 A, u64 X, u64 r4, u64 r5)
+{
+        return (u64)prandom_u32();
+}
+
 /* Register mappings for user programs. */
 #define A_REG           0
 #define X_REG           7
@@ -779,6 +785,7 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
         case SKF_AD_OFF + SKF_AD_NLATTR:
         case SKF_AD_OFF + SKF_AD_NLATTR_NEST:
         case SKF_AD_OFF + SKF_AD_CPU:
+        case SKF_AD_OFF + SKF_AD_RANDOM:
                 /* arg1 = ctx */
                 insn->code = BPF_ALU64 | BPF_MOV | BPF_X;
                 insn->a_reg = ARG1_REG;
@@ -812,6 +819,9 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
                 case SKF_AD_OFF + SKF_AD_CPU:
                         insn->imm = __get_raw_cpu_id - __bpf_call_base;
                         break;
+                case SKF_AD_OFF + SKF_AD_RANDOM:
+                        insn->imm = __get_random_u32 - __bpf_call_base;
+                        break;
                 }
                 break;
 
@@ -1362,6 +1372,7 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
                         ANCILLARY(VLAN_TAG);
                         ANCILLARY(VLAN_TAG_PRESENT);
                         ANCILLARY(PAY_OFFSET);
+                        ANCILLARY(RANDOM);
                         }
 
                         /* ancillary operation unknown or unsupported */
@@ -1746,6 +1757,7 @@ void sk_decode_filter(struct sock_filter *filt, struct sock_filter *to)
                 [BPF_S_ANC_VLAN_TAG]    = BPF_LD|BPF_B|BPF_ABS,
                 [BPF_S_ANC_VLAN_TAG_PRESENT] = BPF_LD|BPF_B|BPF_ABS,
                 [BPF_S_ANC_PAY_OFFSET]  = BPF_LD|BPF_B|BPF_ABS,
+                [BPF_S_ANC_RANDOM]      = BPF_LD|BPF_B|BPF_ABS,
                 [BPF_S_LD_W_LEN]        = BPF_LD|BPF_W|BPF_LEN,
                 [BPF_S_LD_W_IND]        = BPF_LD|BPF_W|BPF_IND,
                 [BPF_S_LD_H_IND]        = BPF_LD|BPF_H|BPF_IND,
diff --git a/tools/net/bpf_exp.l b/tools/net/bpf_exp.l
index bf7be77ddd62..833a96611da6 100644
--- a/tools/net/bpf_exp.l
+++ b/tools/net/bpf_exp.l
@@ -92,6 +92,7 @@ extern void yyerror(const char *str);
 "#"?("cpu")     { return K_CPU; }
 "#"?("vlan_tci") { return K_VLANT; }
 "#"?("vlan_pr") { return K_VLANP; }
+"#"?("rand")    { return K_RAND; }
 
 ":"             { return ':'; }
 ","             { return ','; }
diff --git a/tools/net/bpf_exp.y b/tools/net/bpf_exp.y
index d15efc989ef5..e6306c51c26f 100644
--- a/tools/net/bpf_exp.y
+++ b/tools/net/bpf_exp.y
@@ -56,7 +56,7 @@ static void bpf_set_jmp_label(char *label, enum jmp_type type);
 %token OP_LDXI
 
 %token K_PKT_LEN K_PROTO K_TYPE K_NLATTR K_NLATTR_NEST K_MARK K_QUEUE K_HATYPE
-%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_POFF
+%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_POFF K_RAND
 
 %token ':' ',' '[' ']' '(' ')' 'x' 'a' '+' 'M' '*' '&' '#' '%'
 
@@ -164,6 +164,9 @@ ldb
         | OP_LDB K_POFF {
                 bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0,
                                    SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
+        | OP_LDB K_RAND {
+                bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0,
+                                   SKF_AD_OFF + SKF_AD_RANDOM); }
         ;
 
 ldh
@@ -212,6 +215,9 @@ ldh
         | OP_LDH K_POFF {
                 bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0,
                                    SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
+        | OP_LDH K_RAND {
+                bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0,
+                                   SKF_AD_OFF + SKF_AD_RANDOM); }
         ;
 
 ldi
@@ -265,6 +271,9 @@ ld
         | OP_LD K_POFF {
                 bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0,
                                    SKF_AD_OFF + SKF_AD_PAY_OFFSET); }
+        | OP_LD K_RAND {
+                bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0,
+                                   SKF_AD_OFF + SKF_AD_RANDOM); }
         | OP_LD 'M' '[' number ']' {
                 bpf_set_curr_instr(BPF_LD | BPF_MEM, 0, 0, $4); }
         | OP_LD '[' 'x' '+' number ']' {