ldconfig makes system loader ld-linux.so.2 to be link to 3rd party loader resides in /lib directory on Ubuntu 11.04

[Venkatesh]

ldconfig unlink or removes the existing system loader ld-linux.so that was linked to /lib/i386-linux-gnu/ld-2.13.so and creates symlink with 3rd party loader which resides in /lib/ld-.so, This creates system unusable and gets kernel panic on reboot. This ldconfig behavior can be reproduced when I was doing any pkg installation or upgrade system using apt-get install(Only when 3rd party loaders say for ex. ld-.so present in /lib directory)

Simple General steps to reproduce:
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1) Create shared library loader ld-test.so.2 providing SONAME of system loader that is "ld-linux.so.2" and copy loader ld-test.so.2 to /lib directory
2) Now just run command "ldconfig"
3) after completing ldconfig system is in unusable state that means no commands work, workaround for commands to work is to set LD_LIBRARY_PATH="/lib/i386-linux-gnu" . But kernel panic occurs if we reboot system.

I looked into this issue and then found that what apt-get install is doing and came to know that the ldconfig which is doing this symbolic link to 3rd party loader. Then I gone through ldconfig source code (glibc 2.13) and understood little bit of ldconfig algorithm and came to know that the ldconfig basically searches based on SONAME of each library,Checked our 3rd party library SONAME using "readelf -d /lib/ld-.so.2" utility.

As 3rd party loader ld-.so and system loader /li/ld-linux.so.2 has same SONAME, I am thinking this is causing the ldconfig to link to 3rd party loader. Not sure exactly thats why I have created simple shared library which is having same SONAME as the system loader having and tested the system upgrade using apt-get and then I have encountered into same issue(system unusable) and apt-get upgrade works fine without any issues after creating loader with different SONAME.

But as other versions (Ubuntu 10.xx)or different distribution (RHEl,SLES)of linux works fine with this 3rd party loader having same SONAME, only on this Ubuntu 11.04 creating problem. How is it functioning different here?Is there any specific change with respect to ldconfig loading/linking of 3rd party loaders kept in /lib directory? or having similar SONAME for both loaders creating this problem, if yes then why its not happening on earlier versions? Which is the better place/path in the system to keep 3rd party loaders both in case of a public or private?

Hope above info is enough to understand the issue and appreciate your kind help on this issue.
Please let me know in case if you require any more info.

Thanks and Regards
Venkatesh Prasad C
<email address hidden>

[Adam Conrad (adconrad)]

ldconfig is doing exactly what it was designed to do, which is to link SONAMEs to libraries providing that SONAME in the same directory. This is more a case of "don't do that, then" than a bug in glibc.