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List:       9fans
Subject:    [9fans] passwd(1) over ssh fails: race in telnetd
From:       yaroslav <yarikos () gmail ! com>
Date:       2011-01-26 15:16:17
Message-ID: 1b38321dd9fcb942a015fd7101606737 () isd ! dp ! ua
[Download RAW message or body]

passwd(1), while started on telnetd-simulated /dev/cons (via ssh),
gets killed for writing on closed pipe after "Confirm:" message.  I
think it is because of close()/open() race in
	/sys/src/cmd/ip/telnetd.c:/^conssim/+/open/+/consctl/.
Readln opens and closes consctl, and when two readln calls are made,
next open may be attempted before the daemon reopens of its end of the
simulated consctl.

A fast workaround is injection of sleep(100) between readln calls in
/sys/src/cmd/auth/passwd.c:102.

Suggestions for the proper fix?

- Iaroslav


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