Re: /proc parent &proc_root == NULL?

[John Richard Moser]

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Valdis.Kletnieks@xxxxxx wrote:
> On Wed, 26 Jan 2005 22:35:18 EST, John Richard Moser said:
> 
> 
>>This particular problem pertains to proc_misc.c and trying to create a
>>hook for some grsecurity protections that alter the modes on certain
>>/proc entries.  The chunk of the patch I'm trying to immitate is:
> 
> 
>>+#ifdef CONFIG_GRKERNSEC_PROC_ADD
>>+       create_seq_entry("cpuinfo", gr_mode, &proc_cpuinfo_operations);
>>+#else
>>        create_seq_entry("cpuinfo", 0, &proc_cpuinfo_operations);
>>+#endif
> 
> 
> An alternate way to approach this - leave the permissions alone here.
> 
> And then use the security_ops->inode_permission() hook to do something like:
> 
> 	if ((inode == cpuinfo) && (current->fsuid))
> 		 return -EPERM;
> 
> Writing the proper tests for whether it's the inode you want and whether to
> give the request the kiss-of-death are left as an excersize for the programmer.. ;)
> 
> You may want to use a properly timed initcall() to create a callback that
> happens after proc_misc_init() happens, but before userspace gets going, and
> walk through the /proc tree at that time and cache info on the files you care
> about, so you don't have to re-walk /proc every time permission() gets called....

mmm.  I'd thought about that actually-- for modules to get a whack at
this they'd have to be compiled in.  Loaded as modules would break the
security.

Perhaps both.  I could give modules a "Hook" that gave them a crack at
/proc on load, as well as put a hook in *read**read**read**read*
proc_permission()?  (I wrote one there already!  :)

Also, before it expires

http://rafb.net/paste/results/tZ5Jp878.html

Nice for a simple learning excercise huh?  Modules aren't aware of
stacking, and there's no mandatory dummy code (a la security/dummy.c);
but each hook calls a function that does a loop (based on a C99 variadic
macro) through things, so the lack of a dummy module is kind of offset.

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