1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
|
#include <glib.h>
#include <stdlib.h>
#include <stdio.h>
#include "../src/libslirp.h"
#include "../src/ip6.h"
#include "helper.h"
#include "slirp_base_fuzz.h"
#ifdef CUSTOM_MUTATOR
extern size_t LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize);
size_t LLVMFuzzerCustomMutator(uint8_t *Data, size_t Size, size_t MaxSize, unsigned int Seed);
/// This is a custom mutator, this allows us to mutate only specific parts of
/// the input and fix the checksum so the packet isn't rejected for bad reasons.
extern size_t LLVMFuzzerCustomMutator(uint8_t *Data, size_t Size,
size_t MaxSize, unsigned int Seed)
{
size_t current_size = Size;
uint8_t *Data_ptr = Data;
uint8_t *ip_data;
bool mutated = false;
pcap_hdr_t *hdr = (void *)Data_ptr;
pcaprec_hdr_t *rec = NULL;
if (current_size < sizeof(pcap_hdr_t)) {
return 0;
}
Data_ptr += sizeof(*hdr);
current_size -= sizeof(*hdr);
if (hdr->magic_number == 0xd4c3b2a1) {
g_debug("FIXME: byteswap fields");
return 0;
} /* else assume native pcap file */
if (hdr->network != 1) {
return 0;
}
for ( ; current_size > sizeof(*rec); Data_ptr += rec->incl_len, current_size -= rec->incl_len) {
rec = (void *)Data_ptr;
Data_ptr += sizeof(*rec);
current_size -= sizeof(*rec);
if (rec->incl_len != rec->orig_len) {
return 0;
}
if (rec->incl_len > current_size) {
return 0;
}
if (rec->incl_len < 14 + 1) {
return 0;
}
ip_data = Data_ptr + 14;
if (rec->incl_len >= 14 + 24) {
struct in6_addr *ipsource = (struct in6_addr *) (ip_data + 8);
// This an answer, which we will produce, so don't receive
if (in6_equal(ipsource, &ip6_host) || in6_equal(ipsource, &ip6_dns))
continue;
}
// Exclude packets that are not ICMP from the mutation strategy
if (ip_data[6] != IPPROTO_ICMPV6)
continue;
// Allocate a bit more than needed, this is useful for
// checksum calculation.
uint8_t Data_to_mutate[MaxSize + PSEUDO_IPV6_SIZE];
uint8_t ip_hl_in_bytes = sizeof(struct ip6); /* ip header length */
// Fixme : don't use ip_hl_in_bytes inside the fuzzing code, maybe use the
// rec->incl_len and manually calculate the size.
if (ip_hl_in_bytes > rec->incl_len - 14)
return 0;
uint8_t *start_of_icmp = ip_data + ip_hl_in_bytes;
uint16_t icmp_size = ntohs(*(uint16_t *)(ip_data + 4));
// The size inside the packet can't be trusted, if it is too big it can
// lead to heap overflows in the fuzzing code.
// Fixme : don't use udp_size inside the fuzzing code, maybe use the
// rec->incl_len and manually calculate the size.
if (icmp_size > MaxSize || icmp_size > rec->incl_len - 14 - ip_hl_in_bytes)
return 0;
// Copy interesting data to the `Data_to_mutate` array
// here we want to fuzz everything in icmp
memset(Data_to_mutate, 0, MaxSize + PSEUDO_IPV6_SIZE);
memcpy(Data_to_mutate, start_of_icmp, icmp_size);
// Call to libfuzzer's mutation function.
// For now we dont want to change the header size as it would require to
// resize the `Data` array to include the new bytes inside the whole
// packet.
// This should be easy as LibFuzzer probably does it by itself or
// reserved enough space in Data beforehand, needs some research to
// confirm.
// FIXME: allow up to grow header size to 60 bytes,
// requires to update the `header length` before calculating
// checksum
LLVMFuzzerMutate(Data_to_mutate, icmp_size, icmp_size);
// Set the `checksum` field to 0 and calculate the new checksum
*(uint16_t *)(Data_to_mutate + 2) = 0;
// Copy the source and destination IP addresses, the tcp length and
// protocol number at the end of the `Data_to_mutate` array to calculate
// the new checksum.
memcpy(Data_to_mutate + icmp_size, ip_data + 8, 16*2);
*(Data_to_mutate + icmp_size + 16*2 + 1) = IPPROTO_ICMPV6;
*(Data_to_mutate + icmp_size + 16*2 + 2) = (uint8_t)(icmp_size / 256);
*(Data_to_mutate + icmp_size + 16*2 + 3) = (uint8_t)(icmp_size % 256);
uint16_t new_checksum =
compute_checksum(Data_to_mutate, icmp_size + PSEUDO_IPV6_SIZE);
*(uint16_t *)(Data_to_mutate + 2) = htons(new_checksum);
// Copy the mutated data back to the `Data` array
memcpy(start_of_icmp, Data_to_mutate, icmp_size);
mutated = true;
}
if (!mutated)
return 0;
return Size;
}
#endif // CUSTOM_MUTATOR
|
