Mercurial > dropbear
annotate fuzz/fuzz-sshpacketmutator.c @ 1771:af9ed0815818
Use SSH packet mutator for preauth too
Get rid of separate client mutator.
Have 0.1% chance of llvm random mutation
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author | Matt Johnston <matt@ucc.asn.au> |
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date | Thu, 29 Oct 2020 22:41:37 +0800 |
parents | 3e1e1f82eba6 |
children | 833bf9947603 |
rev | line source |
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1 /* A mutator/crossover for SSH protocol streams. |
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2 Attempts to mutate each SSH packet individually, keeping |
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3 lengths intact. |
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4 It will prepend a SSH-2.0-dbfuzz\r\n version string. |
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5 |
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6 Linking this file to a binary will make libfuzzer pick up the custom mutator. |
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7 |
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8 Care is taken to avoid memory allocation which would otherwise |
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9 slow exec/s substantially */ |
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10 |
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11 #include "fuzz.h" |
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12 #include "dbutil.h" |
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13 |
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14 size_t LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize); |
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15 |
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16 static const char* FIXED_VERSION = "SSH-2.0-dbfuzz\r\n"; |
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17 static const size_t MAX_FUZZ_PACKETS = 500; |
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18 /* XXX This might need tuning */ |
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19 static const size_t MAX_OUT_SIZE = 50000; |
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20 |
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21 /* Splits packets from an input stream buffer "inp". |
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22 The initial SSH version identifier is discarded. |
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23 If packets are not recognised it will increment until an uint32 of valid |
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24 packet length is found. */ |
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25 |
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26 /* out_packets an array of num_out_packets*buffer, each of size RECV_MAX_PACKET_LEN */ |
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27 static void fuzz_get_packets(buffer *inp, buffer **out_packets, unsigned int *num_out_packets) { |
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28 /* Skip any existing banner. Format is |
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29 SSH-protoversion-softwareversion SP comments CR LF |
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30 so we look for SSH-2. then a subsequent LF */ |
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31 unsigned char* version = memmem(inp->data, inp->len, "SSH-2.", strlen("SSH-2.")); |
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32 if (version) { |
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33 buf_incrpos(inp, version - inp->data); |
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34 unsigned char* newline = memchr(&inp->data[inp->pos], '\n', inp->len - inp->pos); |
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35 if (newline) { |
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36 buf_incrpos(inp, newline - &inp->data[inp->pos]+1); |
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37 } else { |
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38 /* Give up on any version string */ |
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39 buf_setpos(inp, 0); |
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40 } |
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41 } |
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42 |
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43 const unsigned int max_out_packets = *num_out_packets; |
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44 *num_out_packets = 0; |
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45 while (1) { |
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46 if (inp->pos + 4 > inp->len) { |
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47 /* End of input */ |
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48 break; |
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49 } |
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50 |
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51 if (*num_out_packets >= max_out_packets) { |
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52 /* End of output */ |
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53 break; |
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54 } |
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55 |
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56 /* Read packet */ |
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57 unsigned int packet_len = buf_getint(inp); |
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58 if (packet_len > RECV_MAX_PACKET_LEN-4) { |
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59 /* Bad length, try skipping a single byte */ |
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60 buf_decrpos(inp, 3); |
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61 continue; |
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62 } |
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63 packet_len = MIN(packet_len, inp->len - inp->pos); |
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64 |
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65 /* Copy to output buffer. We're reusing buffers */ |
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66 buffer* new_packet = out_packets[*num_out_packets]; |
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67 (*num_out_packets)++; |
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68 buf_setlen(new_packet, 0); |
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69 buf_putint(new_packet, packet_len); |
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70 buf_putbytes(new_packet, buf_getptr(inp, packet_len), packet_len); |
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71 buf_incrpos(inp, packet_len); |
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72 } |
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73 } |
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74 |
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75 /* Mutate a packet buffer in-place */ |
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76 static void buf_llvm_mutate(buffer *buf) { |
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77 /* Position it after packet_length and padding_length */ |
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78 const unsigned int offset = 5; |
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79 if (buf->len < offset) { |
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80 return; |
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81 } |
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82 buf_setpos(buf, offset); |
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83 size_t max_size = buf->size - buf->pos; |
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84 size_t new_size = LLVMFuzzerMutate(buf_getwriteptr(buf, max_size), |
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85 buf->len - buf->pos, max_size); |
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86 buf_setpos(buf, 0); |
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87 buf_putint(buf, new_size); |
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88 buf_setlen(buf, offset + new_size); |
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89 } |
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90 |
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91 |
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92 /* Persistent buffers to avoid constant allocations */ |
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93 static buffer *oup; |
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94 static buffer *alloc_packetA; |
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95 static buffer *alloc_packetB; |
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96 buffer* packets1[MAX_FUZZ_PACKETS]; |
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97 buffer* packets2[MAX_FUZZ_PACKETS]; |
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98 |
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99 /* Allocate buffers once at startup. |
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100 'constructor' here so it runs before dbmalloc's interceptor */ |
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101 static void alloc_static_buffers() __attribute__((constructor)); |
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102 static void alloc_static_buffers() { |
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103 |
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104 int i; |
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105 oup = buf_new(MAX_OUT_SIZE); |
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106 alloc_packetA = buf_new(RECV_MAX_PACKET_LEN); |
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107 alloc_packetB = buf_new(RECV_MAX_PACKET_LEN); |
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108 |
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109 for (i = 0; i < MAX_FUZZ_PACKETS; i++) { |
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110 packets1[i] = buf_new(RECV_MAX_PACKET_LEN); |
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111 } |
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112 for (i = 0; i < MAX_FUZZ_PACKETS; i++) { |
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113 packets2[i] = buf_new(RECV_MAX_PACKET_LEN); |
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114 } |
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115 } |
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116 |
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117 size_t LLVMFuzzerCustomMutator(uint8_t *Data, size_t Size, |
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118 size_t MaxSize, unsigned int Seed) { |
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119 |
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120 buf_setlen(alloc_packetA, 0); |
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121 buf_setlen(alloc_packetB, 0); |
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122 buf_setlen(oup, 0); |
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123 |
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124 unsigned int i; |
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125 unsigned short randstate[3] = {0,0,0}; |
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126 memcpy(randstate, &Seed, sizeof(Seed)); |
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127 |
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128 // printhex("mutator input", Data, Size); |
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129 |
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130 /* 0.1% chance straight llvm mutate */ |
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131 if (nrand48(randstate) % 1000 == 0) { |
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132 return LLVMFuzzerMutate(Data, Size, MaxSize); |
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133 } |
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134 |
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135 buffer inp_buf = {.data = Data, .size = Size, .len = Size, .pos = 0}; |
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136 buffer *inp = &inp_buf; |
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137 |
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138 /* Parse packets */ |
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139 unsigned int num_packets = MAX_FUZZ_PACKETS; |
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140 buffer **packets = packets1; |
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141 fuzz_get_packets(inp, packets, &num_packets); |
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142 |
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143 if (num_packets == 0) { |
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144 // gotta do something |
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145 memcpy(Data, FIXED_VERSION, MIN(strlen(FIXED_VERSION), MaxSize)); |
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146 return LLVMFuzzerMutate(Data, Size, MaxSize); |
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147 } |
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148 |
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149 /* Start output */ |
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150 /* Put a new banner to output */ |
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151 buf_putbytes(oup, FIXED_VERSION, strlen(FIXED_VERSION)); |
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152 |
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153 /* Iterate output */ |
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154 for (i = 0; i < num_packets+1; i++) { |
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155 // These are pointers to output |
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156 buffer *out_packetA = NULL, *out_packetB = NULL; |
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157 buf_setlen(alloc_packetA, 0); |
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158 buf_setlen(alloc_packetB, 0); |
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159 |
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160 /* 5% chance each */ |
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161 const int optA = nrand48(randstate) % 20; |
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162 if (optA == 0) { |
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163 /* Copy another */ |
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164 unsigned int other = nrand48(randstate) % num_packets; |
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165 out_packetA = packets[other]; |
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166 } |
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167 if (optA == 1) { |
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168 /* Mutate another */ |
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169 unsigned int other = nrand48(randstate) % num_packets; |
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170 buffer *from = packets[other]; |
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171 buf_putbytes(alloc_packetA, from->data, from->len); |
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172 out_packetA = alloc_packetA; |
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173 buf_llvm_mutate(out_packetA); |
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174 } |
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175 |
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176 if (i < num_packets) { |
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177 int optB = nrand48(randstate) % 10; |
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178 if (optB == 1) { |
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179 /* 10% chance of drop */ |
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180 /* Drop it */ |
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181 // printf("%d drop\n", i); |
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182 } else if (optB <= 6) { |
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183 /* Mutate it, 50% chance */ |
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184 // printf("%d mutate\n", i); |
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185 buffer *from = packets[nrand48(randstate) % num_packets]; |
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186 buf_putbytes(alloc_packetB, from->data, from->len); |
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187 out_packetB = alloc_packetB; |
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188 buf_llvm_mutate(out_packetB); |
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189 } else { |
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190 /* Copy as-is */ |
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191 out_packetB = packets[i]; |
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192 // printf("%d as-is\n", i); |
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193 } |
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194 } |
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195 |
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196 if (out_packetA && oup->len + out_packetA->len <= oup->size) { |
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197 buf_putbytes(oup, out_packetA->data, out_packetA->len); |
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198 } |
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199 if (out_packetB && oup->len + out_packetB->len <= oup->size) { |
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200 buf_putbytes(oup, out_packetB->data, out_packetB->len); |
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201 } |
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202 } |
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203 |
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204 size_t ret_len = MIN(MaxSize, oup->len); |
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205 memcpy(Data, oup->data, ret_len); |
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206 // printhex("mutator done", Data, ret_len); |
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207 return ret_len; |
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208 } |
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209 |
1766 | 210 size_t LLVMFuzzerCustomCrossOver(const uint8_t *Data1, size_t Size1, |
211 const uint8_t *Data2, size_t Size2, | |
212 uint8_t *Out, size_t MaxOutSize, | |
213 unsigned int Seed) { | |
214 unsigned short randstate[3] = {0,0,0}; | |
215 memcpy(randstate, &Seed, sizeof(Seed)); | |
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216 |
1766 | 217 unsigned int i; |
218 buffer inp_buf1 = {.data = (void*)Data1, .size = Size1, .len = Size1, .pos = 0}; | |
219 buffer *inp1 = &inp_buf1; | |
220 buffer inp_buf2 = {.data = (void*)Data2, .size = Size2, .len = Size2, .pos = 0}; | |
221 buffer *inp2 = &inp_buf2; | |
222 | |
223 unsigned int num_packets1 = MAX_FUZZ_PACKETS; | |
224 fuzz_get_packets(inp1, packets1, &num_packets1); | |
225 unsigned int num_packets2 = MAX_FUZZ_PACKETS; | |
226 fuzz_get_packets(inp2, packets2, &num_packets2); | |
227 | |
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228 buf_setlen(oup, 0); |
1766 | 229 /* Put a new banner to output */ |
230 buf_putbytes(oup, FIXED_VERSION, strlen(FIXED_VERSION)); | |
231 | |
232 for (i = 0; i < num_packets1+1; i++) { | |
233 if (num_packets2 > 0 && nrand48(randstate) % 10 == 0) { | |
234 /* 10% chance of taking another packet at each position */ | |
235 int other = nrand48(randstate) % num_packets2; | |
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236 // printf("inserted other packet %d at %d\n", other, i); |
1766 | 237 buffer *otherp = packets2[other]; |
238 if (oup->len + otherp->len <= oup->size) { | |
239 buf_putbytes(oup, otherp->data, otherp->len); | |
240 } | |
241 } | |
242 if (i < num_packets1) { | |
243 buffer *thisp = packets1[i]; | |
244 if (oup->len + thisp->len <= oup->size) { | |
245 buf_putbytes(oup, thisp->data, thisp->len); | |
246 } | |
247 } | |
248 } | |
249 | |
250 size_t ret_len = MIN(MaxOutSize, oup->len); | |
251 memcpy(Out, oup->data, ret_len); | |
252 return ret_len; | |
253 } | |
254 |