openssh connection hangs upon shell exit

[Claude Robitaille]

I am using an openSSH server on a privately built distribution. I am can
login with an interactive session, use scp and everything is fine except
that when I exit the shell of an interactive session or when the copy
transfer terminates (scp), sshd hangs forever. The shell process is in the
zombie state, which indicates that the openssh process for the connection
has not checked the child status.

I understand that using a privately built distribution (distribution may be
not the adequate terms but I have no other) is most certainly the root
cause where some files, privileges, etc. is not set correctly. But I looked
everywhere, including the FAQ on opensssh.com and can not find any useful
guidance.

Any pointers for where to look? Using debug and strace does not help. I can
see 2 errors near the end but I am not sure they are real problem or
related to my issue. Here is the end of this trace (the write \r correspond
to the enter after exit):



write(6, "\r", 1)                       = 1
select(9, [3 4 8], [], NULL, NULL)      = 1 (in [8])
rt_sigprocmask(SIG_BLOCK, [CHLD], [TERM CHLD], 8) = 0
rt_sigprocmask(SIG_SETMASK, [TERM CHLD], NULL, 8) = 0
read(8, "\r\n", 16384)                  = 2
select(9, [3 4 8], [3], NULL, NULL)     = 2 (in [8], out [3])
rt_sigprocmask(SIG_BLOCK, [CHLD], [TERM CHLD], 8) = 0
rt_sigprocmask(SIG_SETMASK, [TERM CHLD], NULL, 8) = 0
read(8, 0x7fff2c252970, 16384)          = -1 EIO (Input/output error)
write(2, "debug2: channel 0: read<=0 rfd 8"..., 41debug2: channel 0:
read<=0 rfd 8 len -1
) = 41
write(2, "debug2: channel 0: read failed\r\n", 32debug2: channel 0: read
failed
) = 32
write(2, "debug2: channel 0: close_read\r\n", 31debug2: channel 0:
close_read
) = 31
close(8)                                = 0
write(2, "debug2: channel 0: input open ->"..., 40debug2: channel 0: input
open -> drain
) = 40
write(3,
"\317\21\213\233\355\n\244`V\264\211\212\307\313\313\213aX\307\324\235\260.H\345T\330_\247\271e\266"...,
48) = 48
write(2, "debug2: channel 0: ibuf empty\r\n", 31debug2: channel 0: ibuf
empty
) = 31
write(2, "debug2: channel 0: send eof\r\n", 29debug2: channel 0: send eof
) = 29
write(2, "debug2: channel 0: input drain -"..., 42debug2: channel 0: input
drain -> closed
) = 42
select(9, [3 4], [3], NULL, NULL)       = 1 (out [3])
rt_sigprocmask(SIG_BLOCK, [CHLD], [TERM CHLD], 8) = 0
rt_sigprocmask(SIG_SETMASK, [TERM CHLD], NULL, 8) = 0
write(3,
"\323m\346\231\252\2024\235\272,<@\325\220$q\231\356\321\37\34\272\ndj\377\332\311:?j\360",
32) = 32
select(9, [3 4], [], NULL, NULLExiting on signal 2
debug1: do_cleanup
debug1: session_pty_cleanup: session 0 release /dev/pts/0
syslogin_perform_logout: logout() returned an error



The read error on fd 8 is probably Ok since I suspect it is the pipe to the
shell, which terminated so an error here is probably normal (BTW, this
shell is busybox).

-- 


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