linux-kernel - Re: [PATCH][Resend v2] Fix infinite loop in search_binary

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Message-Id: <201107042342.HDH34381.OFtHSLOMVFJFOQ@I-love.SAKURA.ne.jp>
Date:	Mon, 4 Jul 2011 23:42:09 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	richard@....at
Cc:	viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH][Resend v2] Fix infinite loop in search_binary_handler()

Richard Weinberger wrote:
> > That's strange... Would you show us printk() output like
> > 
> > 	printk(KERN_INFO "Calling request_module()\n");
> > 	request_module("binfmt-%04x", *(unsigned short *)(&bprm->buf[2]));
> > 	printk(KERN_INFO "Returned from request_module()\n");
> > 
> > for demonstrating that __request_module() cannot stop at
> > MAX_KMOD_CONCURRENT levels of nesting?
> 
> There you go!
> http://userweb.kernel.org/~rw/boot.log
> 
> I did not count all messages, but they are more than 50. :-)

Thank you.

$ grep -F 'Calling request_module()' boot.log | wc -l
25819
$ grep -F 'Returned from request_module()' boot.log | wc -l
25770

So, __request_module() is stopping at MAX_KMOD_CONCURRENT levels
of nesting. Eventually the process that triggered the first
request_module() will return from search_binary_handler().
I don't think this is an infinite loop inside search_binary_handler().

But it would look like an infinite loop bug if the caller of execve()
repeats forever. Printing additional information like

  printk(KERN_INFO "Calling request_module() %s %d %s %d %d\n", current->comm,
         current->pid, bprm->filename, bprm->argc, bprm->envc);

would help.
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