0000891: Segfault in snmpd apparantly caused by non initialised shared library BSS

BusyBox Bug and Patch Tracking

Viewing Issue Simple Details [ Jump to Notes ]

[ View Advanced ] [ Issue History ] [ Print ]

Category

Severity

Reproducibility

Date Submitted

Last Update

0000891

[buildroot] Shared Library Support

major

sometimes

06-01-06 08:45

02-12-07 05:34

Reporter

mfuzzey

View Status

public

Assigned To

buildroot

Priority

normal

Resolution

open

Status

assigned

Product Version

0.9.27

Summary

0000891: Segfault in snmpd apparantly caused by non initialised shared library BSS

Description

net-snmpd 5.1.2 built with buildroot sometimes segfaults on startup.
Once this occurs it is 100% reproducable until reboot...

Prelimery investigation points to uClibc shared library support (but I may be wrong...)

Segfault occurs because external_signal_scheduled[] and external_signal_handler[] defined in agents/agent_registry.c and compiled to libnetsnmpagent.so are not initialised but the code assumes they are zero filled on startup.

Additional Information

Adding code to start main() in snmpd.c:
    printf("table at %p\n", external_signal_scheduled);
        for (i = 0; i < NUM_EXTERNAL_SIGS; i++) {
        printf("init signal %d scheduled=%d handler=%p\n", i, external_signal_scheduled[i], external_signal_handler[i]);
        }

Output:
table at 0x16ba8
init signal 0 scheduled=0 handler=(nil)
...
init signal 10 scheduled=-1 handler=(nil)
init signal 11 scheduled=67174399 handler=(nil)
...

Manually zeroing the tables in main() "fixes" the problem.

The load address reported above agrees with readelf :
mfuzzey@dhcp78-150:~$ readelf snmpd -a | grep external_signal_scheduled
    96: 00016ba8 128 OBJECT GLOBAL DEFAULT 21 external_signal_scheduled

Which is indeed in BSS:
:~/$ readelf snmpd -S | grep bss
  [21] .bss NOBITS 000167f4 0067f4 00167c 00 WA 0 0 8

Attached Files

Relationships

Notes
(0001910) bernhardf 12-22-06 03:06	Please provide a package/netsnmp/netsnmp-5.2.1-fix-extern-initializers.patch that corrects this bug in netsnmp. Make sure to send the patch upstream too. TIA,

Issue History
Date Modified	Username	Field	Change
06-01-06 08:45	mfuzzey	New Issue
06-01-06 08:45	mfuzzey	Status	new => assigned
06-01-06 08:45	mfuzzey	Assigned To	=> uClibc
06-01-06 09:06	mfuzzey	Issue Monitored: mfuzzey
12-22-06 03:06	bernhardf	Note Added: 0001910
12-22-06 03:06	bernhardf	Status	assigned => feedback
02-12-07 05:34	vapier	Status	feedback => assigned
02-12-07 05:34	vapier	Assigned To	uClibc => buildroot