uuid_generate calls system rng (not thread safe?)

[Kevin Martin]

Hi,

libgearman calls uuid_generate from libuuid which uses the system pseudo rng. See the below stack trace. It might be helpful to add some documentation that this happens - it's certainly caused us a few days of being baffled.

Also, given that uuid_generate uses the system RNG, it does not seem thread safe. Does this affect the thread safety of libgearman?

In libuuid, uuid_generate in gen_uuid.c calls random_get_bytes(). This is implemented in lib/randutils.c which is where the calls to the system rng are:

https://github.com/karelzak/util-linux/blob/master/lib/randutils.c (lines 41, 51, 89)

Note rand() and srand() may be #defined in https://github.com/karelzak/util-linux/blob/master/include/randutils.h

Thanks,
Kevin

Stack trace is from Gearman 0.29 I think, but I checked the latest trunk and uuid_generate is called on line 158

Breakpoint 1, 0x00007ffff1daace0 in srandom () from /lib/libc.so.6
(gdb) bt
#0 0x00007ffff1daace0 in srandom () from /lib/libc.so.6
#1 0x00007ffff067f866 in ?? () from /lib/libuuid.so.1
#2 0x00007ffff0680729 in uuid_generate () from /lib/libuuid.so.1
#3 0x00007ffff4a5f515 in add_task (client=..., task=0x7fffffffd770,
    context=0x0, command=GEARMAN_COMMAND_SUBMIT_JOB, function=..., unique=...,
    workload=..., when=0, actions=...) at libgearman/add.cc:180
#4 0x00007ffff4a60237 in _client_do (client=0x721ab0,
    command=GEARMAN_COMMAND_SUBMIT_JOB,
    function_name=0x71bbd8 "convscript_retrieve", unique=0x0,
    workload_str=0x71b028, workload_size=37, result_size=0x7fffffffdae8,
    ret_ptr=0x7fffffffdae4) at libgearman/client.cc:147
#5 0x00007ffff4a60ea0 in gearman_client_do (client=0x721ab0,
    function=0x71bbd8 "convscript_retrieve", unique=0x0, workload=0x71b028,
    workload_size=37, result_size=0x7fffffffdae8, ret_ptr=0x7fffffffdae4)
    at libgearman/client.cc:598

[Brian Aker (brianaker)]

Thanks. The uuid call is not technically required, I'll add an option to make it optional.

[Brian Aker (brianaker)]

I spoke to the author of libuuid and he confirmed that there is an issue with libuuid and thread safety. He mentioned a solution using the uuidd daemon. I am asking him for more details about this.

Thanks,
    -Brian

[Brian Aker (brianaker)]

The fix will be to use uuid_generate_time_safe(), and document that the uuidd daemon needs to be running.

[Kevin Martin (kev82)]

Ok, that's great. Thankyou.