replace the OpenBSD fd_set sizing code with something more efficient.

Only call malloc() if the fd is too big for the compiled in fd_set size,
and don't use calloc either.  This should reduce the impact of conflicts
with private malloc implementations etc.  When using the fd_set on the
stack, only zero what is needed rather than all 1024 bits like FD_ZERO did.

1 files changed, 16 insertions, 9 deletions

diff --git a/lib/libc/net/res_send.c b/lib/libc/net/res_send.c
index 798d0f6..9061ec6 100644
--- a/lib/libc/net/res_send.c
+++ b/lib/libc/net/res_send.c
@@ -56,7 +56,7 @@
 #if defined(LIBC_SCCS) && !defined(lint)
 static char sccsid[] = "@(#)res_send.c	8.1 (Berkeley) 6/4/93";
 static char orig_rcsid[] = "From: Id: res_send.c,v 8.13 1997/06/01 20:34:37 vixie Exp";
-static char rcsid[] = "$Id: res_send.c,v 1.16 1997/06/27 08:22:03 peter Exp $";
+static char rcsid[] = "$Id: res_send.c,v 1.17 1997/06/27 13:00:51 peter Exp $";
 #endif /* LIBC_SCCS and not lint */
 
 /*
@@ -469,7 +469,8 @@ read_len:
 			 * Use datagrams.
 			 */
 			struct timeval timeout;
-			fd_set *dsmaskp;
+			fd_set dsmask, *dsmaskp;
+			int dsmasklen;
 			struct sockaddr_in from;
 			int fromlen;
 
@@ -575,16 +576,22 @@ read_len:
 				timeout.tv_sec = 1;
 			timeout.tv_usec = 0;
     wait:
-			dsmaskp = (fd_set *)calloc(howmany(s+1, NFDBITS),
-						   sizeof(fd_mask));
-			if (dsmaskp == NULL) {
-				res_close();
-				goto next_ns;
-			}
+			dsmasklen = howmany(s+1, NFDBITS) * sizeof(fd_mask);
+			if (dsmasklen > sizeof(fd_set)) {
+				dsmaskp = (fd_set *)malloc(dsmasklen);
+				if (dsmaskp == NULL) {
+					res_close();
+					goto next_ns;
+				}
+			} else
+				dsmaskp = &dsmask;
+			/* only zero what we need */
+			bzero((char *)dsmaskp, dsmasklen);
 			FD_SET(s, dsmaskp);
 			n = select(s+1, dsmaskp, (fd_set *)NULL,
 				   (fd_set *)NULL, &timeout);
-			free(dsmaskp);
+			if (dsmaskp != &dsmask)
+				free(dsmaskp);
 			if (n < 0) {
 				if (errno == EINTR)
 					goto wait;