Vendored libslirp (#2045)

Add vendored libslirp into the repo with a shim to remove its dependency on glib.

src/frontend/libslirp/fuzzing/slirp_fuzz_icmp6.c

@@ -0,0 +1,134 @@
+#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