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
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