Dereferencing nullptr in oldChannelNotify.cpp

[Dominik]

Hello,

I monitor a variable using EPICSv4 via the "channel access" protocol and stumbled over this segmentation violation.

Linux x86_64
base-3.15.4
EPICS-CPP-4.5.0.2

```
#0 ca_element_count (pChan=0x0) at ../oldChannelNotify.cpp:634
#1 0x00007ffff77ed30a in epics::pvAccess::ca::CAChannel::connected (this=0x67c450) at ../../src/ca/caChannel.cpp:164
#2 0x00007ffff7ddd73e in oldChannelNotify::connectNotify (this=0x67c750, guard=...) at ../oldChannelNotify.cpp:93
#3 0x00007ffff7dce4c3 in nciu::connect (this=this@entry=0x7ffff03c7010, nativeType=6, nativeCount=1, sidIn=sidIn@entry=1, guard=...) at ../nciu.cpp:159
#4 0x00007ffff7dbd36a in cac::createChannelRespAction (this=<optimized out>, mgr=..., iiu=..., hdr=...) at ../cac.cpp:1138
#5 0x00007ffff7dd56c6 in tcpiiu::processIncoming (this=0x7fffcc0008c0, currentTime=..., mgr=...) at ../tcpiiu.cpp:1254
#6 0x00007ffff7dd7959 in tcpRecvThread::run (this=0x7fffcc0009a8) at ../tcpiiu.cpp:521
#7 0x00007ffff68670a9 in epicsThreadCallEntryPoint (pPvt=0x7fffcc0009b0) at ../../../src/libCom/osi/epicsThread.cpp:85
#8 0x00007ffff686cbcc in start_routine (arg=0x7fffcc00a3a0) at ../../../src/libCom/osi/os/posix/osdThread.c:403
#9 0x000000305ac07aa1 in start_thread () from /lib64/libpthread.so.0
#10 0x000000305a8e893d in clone () from /lib64/libc.so.6
```

It is triggered when the PV comes online while the program is already trying to connect to it.

Best regards
Dominik

[Andrew Johnson (anj)]

Hi Dominik,

I think this problem may be due to a known bug in EPICS-CPP-4.5.0.2 which has been fixed in the latest 4.6.0 release, see https://github.com/epics-base/pvAccessCPP/issues/53 if you want to read the developers' discussions about it. Can you update your version of EPICS V4 to 4.6.0 and see if the problem still exists?

Thanks,

- Andrew