netcat may read from invalid file descriptors

[leahneukirchen]

This is a minor issue, but could be avoided easily. When any socket in the poll loop errored, the fd is set to -1 in

openbsd/src/usr.bin/nc/netcat.c

Line 1164 in 1c25761

if (pfd[n].revents & (POLLERR|POLLNVAL)) {

, however this does not stop later code from calling fillbuf on it, e.g.

openbsd/src/usr.bin/nc/netcat.c

Line 1233 in 1c25761

ret = fillbuf(pfd[POLL_NETIN].fd, netinbuf,

I suggest readbuf detects fd == -1 and just returns -1 then.

Can be reproduced on Linux with an asynchronous connect that has SO_LINGER set (but probably many ways):

accept4(3, {sa_family=AF_INET, sin_port=htons(39058), sin_addr=inet_addr("127.0.0.1")}, [128 => 16], SOCK_NONBLOCK) = 4
poll([{fd=0, events=POLLIN}, {fd=4, events=0}, {fd=4, events=POLLIN}, {fd=1, events=0}], 4, -1) = 2 ([{fd=4, revents=POLLERR|POLLHUP}, {fd=4, revents=POLLIN|POLLERR|POLLHUP}])
read(-1, 0x7ffe6a792790, 16384)         = -1 EBADF (Bad file descriptor)