Created on 2017-04-17 14:18 by Chinh Nguyen, last changed 2017-04-17 14:18 by Chinh Nguyen.
|msg291798 - (view)||Author: Chinh Nguyen (Chinh Nguyen)||Date: 2017-04-17 14:18|
I'm using ctypes to access the PAM library to change a user's password. That is, using the function pam_chauthtok. This is occurring inside a python celery worker in FreeBSD. This will work the first time, the second time generates a segfault and crashes the worker. On attaching gdb to the worker process, I observe the following: * Crash occurs in function login_setcryptfmt * Setting a breakpoint there, I see the following after the first successful password change "warning: Temporarily disabling breakpoints for unloaded shared library "/lib/libcrypt.so.5" * When there is segfault on the second password change, the location of the segfault cannot be disassemble * It doesn't look like libcrypt is a direct dependency of libpam. So it looks like what is happening is this: * libcrypt is loaded (by python/system?) to invoke some password-related functions, it is then unloaded (by python/system?) * When the same function is invoked again, somehow libcrypt does not get loaded. This results in a function call to the same function address which is now invalid. My current work-around is to include libcrypto explicitly by binding to it though I don't use it directly. For example, libcrypt = CDLL(find_library("crypt")). Other notes: * This does not occur if I launch celery worker all running in the same process via the celery "green threads" module eventlet * This only happens if the celery worker is a python child process. I don't know how celery spawns child processes.
|2017-04-17 14:18:15||Chinh Nguyen||create|