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use poll rather than select in dns lookups (also clock_gettime) 

if the file descriptor resource limit has been increased past
FD_SETSIZE, this is actually a security issue; we could write past the
end of the fd_set object. using poll makes it a non-issue, and
simplifies the code at the same time.

also, use clock_gettime instead of gettimeofday, for reduced bloat
and better entropy.
This commit is contained in:
Rich Felker 2011-09-21 23:17:45 -04:00
parent 81a5577a86
commit bf027ca5e0
1 changed files with 10 additions and 12 deletions
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22
src/network/__dns.c
View File

@ -5,8 +5,7 @@
#include <limits.h> #include <limits.h>
#include <string.h> #include <string.h>
#include <sys/socket.h> #include <sys/socket.h>
#include <sys/select.h> #include <poll.h>
#include <sys/time.h>
#include <netinet/in.h> #include <netinet/in.h>
#include <time.h> #include <time.h>
#include <ctype.h> #include <ctype.h>
@ -16,7 +15,7 @@
#include "stdio_impl.h" #include "stdio_impl.h"
#define TIMEOUT 5 #define TIMEOUT 5
#define RETRY 1 #define RETRY 1000
#define PACKET_MAX 512 #define PACKET_MAX 512
#define PTR_MAX (64 + sizeof ".in-addr.arpa") #define PTR_MAX (64 + sizeof ".in-addr.arpa")
@ -40,8 +39,8 @@ int __dns_doqueries(unsigned char *dest, const char *name, int *rr, int rrcnt)
int got = 0, failed = 0; int got = 0, failed = 0;
int errcode = EAI_AGAIN; int errcode = EAI_AGAIN;
int i, j; int i, j;
struct timeval tv; struct timespec ts;
fd_set fds; struct pollfd pfd;
int id; int id;
int cs; int cs;
@ -58,8 +57,8 @@ int __dns_doqueries(unsigned char *dest, const char *name, int *rr, int rrcnt)
ql = i+4; ql = i+4;
/* Make a reasonably unpredictable id */ /* Make a reasonably unpredictable id */
gettimeofday(&tv, 0); clock_gettime(CLOCK_REALTIME, &ts);
id = tv.tv_usec + tv.tv_usec/256 & 0xffff; id = ts.tv_nsec + ts.tv_nsec/65536UL & 0xffff;
/* Get nameservers from resolv.conf, fallback to localhost */ /* Get nameservers from resolv.conf, fallback to localhost */
f = __fopen_rb_ca("/etc/resolv.conf", &_f, _buf, sizeof _buf); f = __fopen_rb_ca("/etc/resolv.conf", &_f, _buf, sizeof _buf);
@ -94,6 +93,9 @@ int __dns_doqueries(unsigned char *dest, const char *name, int *rr, int rrcnt)
/* Nonblocking to work around Linux UDP select bug */ /* Nonblocking to work around Linux UDP select bug */
fcntl(fd, F_SETFL, fcntl(fd, F_GETFL, 0) | O_NONBLOCK); fcntl(fd, F_SETFL, fcntl(fd, F_GETFL, 0) | O_NONBLOCK);
pfd.fd = fd;
pfd.events = POLLIN;
/* Loop until we timeout; break early on success */ /* Loop until we timeout; break early on success */
for (; time(0)-t0 < TIMEOUT; ) { for (; time(0)-t0 < TIMEOUT; ) {
@ -106,11 +108,7 @@ int __dns_doqueries(unsigned char *dest, const char *name, int *rr, int rrcnt)
} }
/* Wait for a response, or until time to retry */ /* Wait for a response, or until time to retry */
FD_ZERO(&fds); if (poll(&pfd, 1, RETRY) <= 0) continue;
FD_SET(fd, &fds);
tv.tv_sec = RETRY;
tv.tv_usec = 0;
if (select(fd+1, &fds, 0, 0, &tv) <= 0) continue;
/* Process any and all replies */ /* Process any and all replies */
while (got+failed < rrcnt && (rlen = recvfrom(fd, r, 512, 0, while (got+failed < rrcnt && (rlen = recvfrom(fd, r, 512, 0,