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Switch from pcap_next to pcap_next_ex to check for errors

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This change supports #1394. When the network goes down, Nmap ought to
stop instead of slowing to an infinite crawl.
This commit is contained in:
dmiller
2020-01-13 17:14:45 +00:00
parent dcf4aa9f78
commit 00cb4d22d9
2 changed files with 63 additions and 35 deletions
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57
tcpip.cc
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@@ -1551,8 +1551,9 @@ char *readipv4_pcap(pcap_t *pd, unsigned int *len, long to_usec,
char *readip_pcap(pcap_t *pd, unsigned int *len, long to_usec,
struct timeval *rcvdtime, struct link_header *linknfo, bool validate) {
unsigned int offset = 0;
struct pcap_pkthdr head;
char *p;
struct pcap_pkthdr *head;
const unsigned char *p;
int pcap_status = 0;
int datalink;
int timedout = 0;
struct timeval tv_start, tv_end;
@@ -1651,18 +1652,22 @@ char *readip_pcap(pcap_t *pd, unsigned int *len, long to_usec,
break;
#endif
default:
p = (char *) pcap_next(pd, &head);
if (head.caplen == 0) {
pcap_status = pcap_next_ex(pd, &head, &p);
if (pcap_status == 0) {
/* Lets sleep a brief time and try again to increase the chance of seeing
a real packet ... */
usleep(500000);
p = (char *) pcap_next(pd, &head);
pcap_status = pcap_next_ex(pd, &head, &p);
}
if (head.caplen > 100000) {
fatal("FATAL: %s: bogus caplen from libpcap (%d) on interface type %d", __func__, head.caplen, datalink);
if (pcap_status != 1 || !head) {
// No packet captured
fatal("FATAL: Unknown datalink type (%d).", datalink);
}
error("FATAL: Unknown datalink type (%d). Caplen: %d; Packet:", datalink, head.caplen);
nmap_hexdump((unsigned char *) p, head.caplen);
if (head->caplen > 100000 || !p) {
fatal("FATAL: %s: bogus caplen from libpcap (%d) on interface type %d", __func__, head->caplen, datalink);
}
error("FATAL: Unknown datalink type (%d). Caplen: %d; Packet:", datalink, head->caplen);
nmap_hexdump(p, head->caplen);
exit(1);
}
@@ -1673,6 +1678,7 @@ char *readip_pcap(pcap_t *pd, unsigned int *len, long to_usec,
do {
p = NULL;
pcap_status = 0;
/* It may be that protecting this with !pcap_selectable_fd_one_to_one is not
necessary, that it is always safe to do a nonblocking read in this way on
all platforms. But I have only tested it on Solaris. */
@@ -1683,21 +1689,32 @@ char *readip_pcap(pcap_t *pd, unsigned int *len, long to_usec,
assert(nonblock == 0);
rc = pcap_setnonblock(pd, 1, NULL);
assert(rc == 0);
p = (char *) pcap_next(pd, &head);
pcap_status = pcap_next_ex(pd, &head, &p);
rc = pcap_setnonblock(pd, nonblock, NULL);
assert(rc == 0);
}
if (p == NULL) {
/* Nonblocking pcap_next didn't get anything. */
if (pcap_status == PCAP_ERROR) {
// TODO: Gracefully end the scan.
// For now, consider a pcap read error to be fatal.
fatal("Error from pcap_next_ex: %s\n", pcap_geterr(pd));
}
if (pcap_status == 0 || p == NULL) {
/* Nonblocking pcap_next_ex didn't get anything. */
if (pcap_select(pd, to_usec) == 0)
timedout = 1;
else
p = (char *) pcap_next(pd, &head);
pcap_status = pcap_next_ex(pd, &head, &p);
}
if (p) {
if (head.caplen <= offset) {
if (pcap_status == PCAP_ERROR) {
// TODO: Gracefully end the scan.
fatal("Error from pcap_next_ex: %s\n", pcap_geterr(pd));
}
if (pcap_status == 1 && p) {
if (head->caplen <= offset) {
*len = 0;
return NULL;
}
@@ -1709,7 +1726,7 @@ char *readip_pcap(pcap_t *pd, unsigned int *len, long to_usec,
}
p += offset;
}
if (!p) {
else {
/* Should we timeout? */
if (to_usec == 0) {
timedout = 1;
@@ -1726,7 +1743,7 @@ char *readip_pcap(pcap_t *pd, unsigned int *len, long to_usec,
*len = 0;
return NULL;
}
*len = head.caplen - offset;
*len = head->caplen - offset;
if (*len > alignedbufsz) {
alignedbuf = (char *) safe_realloc(alignedbuf, *len);
alignedbufsz = *len;
@@ -1752,9 +1769,9 @@ char *readip_pcap(pcap_t *pd, unsigned int *len, long to_usec,
gettimeofday(&tv_end, NULL);
*rcvdtime = tv_end;
#else
rcvdtime->tv_sec = head.ts.tv_sec;
rcvdtime->tv_usec = head.ts.tv_usec;
assert(head.ts.tv_sec);
rcvdtime->tv_sec = head->ts.tv_sec;
rcvdtime->tv_usec = head->ts.tv_usec;
assert(head->ts.tv_sec);
#endif
}