linux-kernel - Re: [RFC] kobject: add kobject_init_ng and kobject_init_and

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 30 Nov 2007 15:25:52 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Greg KH <greg@...ah.com>
cc:	Cornelia Huck <cornelia.huck@...ibm.com>,
	Kay Sievers <kay.sievers@...y.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Jonathan Corbet <corbet@....net>,
	Randy Dunlap <randy.dunlap@...cle.com>
Subject: Re: [RFC] kobject: add kobject_init_ng and kobject_init_and_add
 functions

On Fri, 30 Nov 2007, Greg KH wrote:

> +/**
> + * kobject_init_and_add - initialize a kobject structure and add it to the kobject hierarchy
> + * @kobj: pointer to the kobject to initialize
> + * @ktype: pointer to the ktype for this kobject.
> + * @parent: pointer to the parent of this kobject.
> + * @fmt: the name of the kobject.
> + *
> + * This function will properly initialize a kobject and then call
> + * kobject_add().
> + *
> + * If the function returns an error, the memory allocated by the kobject
> + * can be safely freed, no other functions need to be called.
> + */
> +int kobject_init_and_add(struct kobject *kobj, struct kobj_type *ktype,
> +			 struct kobject *parent, const char *fmt, ...)
> +{
> +	va_list args;
> +	int retval;
> +
> +	va_start(args, fmt);
> +	retval = kobject_init_varg(kobj, ktype, parent, fmt, args);
> +	va_end(args);
> +	if (retval)
> +		return retval;
> +
> +	retval = kobject_add(kobj);
> +	if (retval)
> +		kobject_put(kobj);

No, no!

You have recreated the problem we have been discussing during the last
couple of days.  If the kobject_init_varg() routine gets an error then
the kobject will need to be deallocated manually.  If the kobject_add()
routine gets an error then the cleanup invoked by kobject_put() will do
the deallocation automatically.

But the caller can't tell in which subroutine an error occurred, so it
won't know what to do when kobject_init_and_add() returns an error.

The only way to resolve this problem is to have the _init routine 
consume no resources and never fail.  That way the only possible 
failure mode would be if the _add routine doesn't work, in which case 
either a kfree() or a kobject_put() would be acceptable.

In particular, this implies that the name should be set as part of the 
_add() call, not as part of _init().  This is more in line with the way 
the code tends to use kobjects anyhow.  Unless people want to name 
unregistered kobjects -- does this ever happen?  And it if does, can 
these kobjects simply be replaced by krefs?

My suggestion: Have kobject_init_ng() accept a ktype pointer but not a 
parent or name.  Instead, make kobject_add_ng() take the parent and 
name (possibly a kset also).  Then when kobject_init_and_add() 
encounters an error, it shouldn't do a _put() -- the caller can either 
do the _put() or just do a kfree().

Alan Stern

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/