When an underlying ioctl(2) handler returns an error, our ioctl(2)

interface considers that it hits a fatal error, and will not copyout
the request structure back for _IOW and _IOWR ioctls, keeping them
untouched.

The previous implementation of the SIOCGIFDESCR ioctl intends to
feed the buffer length back to userland.  However, if we return
an error, the feedback would be defeated and ifconfig(8) would
trap into an infinite loop.

This commit changes SIOCGIFDESCR to set buffer field to NULL to
indicate the previous ENAMETOOLONG case.

Reported by:	bschmidt
MFC after:	2 weeks

1 files changed, 12 insertions, 11 deletions

diff --git a/sbin/ifconfig/ifconfig.c b/sbin/ifconfig/ifconfig.c
index 7af3306..aa96175 100644
--- a/sbin/ifconfig/ifconfig.c
+++ b/sbin/ifconfig/ifconfig.c
@@ -922,19 +922,20 @@ status(const struct afswtch *afp, const struct sockaddr_dl *sdl,
 			ifr.ifr_buffer.buffer = descr;
 			ifr.ifr_buffer.length = descrlen;
 			if (ioctl(s, SIOCGIFDESCR, &ifr) == 0) {
-				if (strlen(descr) > 0)
-					printf("\tdescription: %s\n", descr);
-				break;
-			} else if (errno == ENAMETOOLONG)
-				descrlen = ifr.ifr_buffer.length;
-			else
-				break;
-		} else {
+				if (ifr.ifr_buffer.buffer == descr) {
+					if (strlen(descr) > 0)
+						printf("\tdescription: %s\n",
+						    descr);
+				} else if (ifr.ifr_buffer.length > descrlen) {
+					descrlen = ifr.ifr_buffer.length;
+					continue;
+				}
+			}
+		} else
 			warn("unable to allocate memory for interface"
 			    "description");
-			break;
-		}
-	};
+		break;
+	}
 
 	if (ioctl(s, SIOCGIFCAP, (caddr_t)&ifr) == 0) {
 		if (ifr.ifr_curcap != 0) {