[Bug 3598] New: Dead lock of sshd and Defunct of sshd

bugzilla-daemon at mindrot.org bugzilla-daemon at mindrot.org
Thu Aug 3 22:51:50 AEST 2023


            Bug ID: 3598
           Summary: Dead lock of sshd and Defunct of sshd
           Product: Portable OpenSSH
           Version: 9.1p1
          Hardware: ix86
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: sshd
          Assignee: unassigned-bugs at mindrot.org
          Reporter: mark.zhang at nokia-sbell.com

Hello expert,

Recently, we encountered one scenario like:
1) login by root from remote.
2) with default loglevel(INFO) of sshd, it will print one log to
auth.log by syslog (got one lock here).
3) But there was some problem that blocked the print action in step-2 a
long time, more than 90 seconds.
4) The timer of LoginGraceTime(default 90 seconds) fired, then tiggered
one another log.
5) Sshd try to get the lock,  as the same lock that has been stuck in
step 2.
6) Then the dead lock happened on sshd
7) Also caused the zombie process of the other sshd.

Please help confirm.
And any thing could be done from sshd to avoid dead lock. That may
cause number of process/used memory kept increasing, when ssh login
keep trying from outside.

(gdb) bt
#0  __kernel_vsyscall () at arch/x86/entry/vdso/vdso32/system_call.S:72
#1  0xf7956c82 in __lll_lock_wait_private () at
#2  0xf7a2f394 in openlog (ident=0x5812c1a0 "sshd", logstat=1,
logfac=32) at ../misc/syslog.c:384
#3  0x565e99ac in do_log ()
#4  0x565e9cf4 in sshlogv ()
#5  0x565e9b29 in sshsigdie ()
#6  0x56585084 in grace_alarm_handler ()
#7  <signal handler called>
#8  __kernel_vsyscall () at arch/x86/entry/vdso/vdso32/system_call.S:72
#9  0xf7a336b1 in __libc_send (fd=5, buf=0x581644e0, len=153,
flags=16384) at ../sysdeps/unix/sysv/linux/send.c:30
#10 0xf7a2f08c in _GI__vsyslog_chk (pri=<optimized out>,
flag=<optimized out>, fmt=<optimized out>, ap=<optimized out>) at
#11 0xf7a2f2fb in __syslog (pri=6, fmt=0x56641418 "%.500s") at
#12 0x565e99cb in do_log ()
#13 0x565e9cf4 in sshlogv ()
#14 0x565e9a52 in sshlog ()
#15 0x5659a291 in auth_log ()
#16 0x565ad53b in monitor_child_preauth ()
#17 0x5658565b in privsep_preauth ()
#18 0x5658ae6d in main ()


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