spinlock in centos 6.4 and redhat enterprise 6 using chcon

[Stefano Borini <stefano.borini@quantumwise.com>]

Good morning,

I am encountering what seems to be a spinlock with the chcon utility 
trying the following operation

chcon -t texrel_shlib_t /tmp/subdir/withheldpath

where withheld path is a .so that is going to be accessed with dlopen.
I am not invoking the chcon command directly nor performing the dlopen, 
a closed-source library does that, apparently to prepare the .so for 
dlopening.

Note that if I try the same operation from the command line, even while 
the spinlock is in progress, no lock occurs.

I am unable to understand the details of what may cause this spinlock. 
This is the backtrace of chcon, apparently involving some thread local 
storage

#0  0x0000003e3ea00b64 in rtld_lock_default_lock_recursive () from 
/lib64/ld-linux-x86-64.so.2
#1  0x0000003e3ea11257 in tls_get_addr_tail () from 
/lib64/ld-linux-x86-64.so.2
#2  0x0000003e3ea11660 in __tls_get_addr () from /lib64/ld-linux-x86-64.so.2
#3  0x0000003e40a14334 in selinux_raw_to_trans_context () from 
/lib64/libselinux.so.1
#4  0x0000003e40a0ca7a in getfilecon () from /lib64/libselinux.so.1

Checking the tls_get_addr_tail function, it is apparently stuck in the 
again: loop

http://code.woboq.org/userspace/glibc/elf/dl-tls.c.html#742

I have only access to the centos 6.4 and can run additional 
non-destructive tests if needed. It's a customer machine so I am unable 
to say if modifications have been done to it when it comes to security, 
although I suspect it's a standard centos6.4 installation with selinux 
enabled.

The current ls -Z of /tmp gives

system_u:object_r:tmp_t:s0

of subdir and of the so file is

unconfined_u:object_r:user_tmp_t:s0

Thank you for your help.


-- 
Stefano Borini
QuantumWise A/S