Messages in this thread | | | Date | Tue, 25 Feb 2014 15:46:43 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] Change task_struct->comm to use RCU. |
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On Tue, Feb 25, 2014 at 09:54:01PM +0900, Tetsuo Handa wrote: > Lai Jiangshan wrote: > > CC scheduler people. > > > > I can't figure out what we get with this patch. > > > OK. Welcome to this thread. I'll explain you what is going on. > > Current problem: > > printk("%s\n", task->comm) is racy because "%s" format specifier assumes that > the corresponding argument does not change between strnlen() and the for loop > at string() in lib/vsnprintf.c . If task->comm was "Hello Linux" until > strnlen() and becomes "Penguin" before the for loop, "%s" will emit > "Penguin\0nux" (note the unexpected '\0' byte and the garbage bytes).
I would have actually expected it to stop emitting chars at \0. But sure. Couldn't care less though; that's what you get, we all know this, we've all been through this discussion several times. Get over it already.
One of the last threads on this is:
https://lkml.org/lkml/2011/5/17/516
> Likewise, audit_log_untrustedstring(ab, current->comm) is racy. > If task->comm was "Hello Linux" until audit_string_contains_control() in > audit_log_n_untrustedstring() returns false, and becomes "Penguin" before > memcpy() in audit_log_n_string() is called, memcpy() will emit "Penguin\0nux" > into the audit log, which results in loss of information (e.g. SELinux > context) due to the unexpected '\0' byte.
I expect the audit people don't like this? Also, how do audit and the LSM crap things interact? I thought they were both different piles of ignorable goo?
See there's not actually a problem statement here at all, so you can't go about proposing solutions quite yet.
> Proposed solution: > > To fix abovementioned problem, I proposed commcpy() and "%pT" format > specifier which does > > char tmp[16]; > memcpy(tmp, task->comm, 16); > tmp[15] = '\0'; > sprintf(buf, "%s", tmp); > > instead of > > sprintf(buf, "%s", task->comm); > > .
How about you do what you're supposed to do when you want a reliable ->comm and use get_task_comm()?
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