linux-kernel - Re: 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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <d7c1a000-ca47-bace-c098-d3f3ab0c5127@yandex-team.ru>
Date:   Tue, 2 Jun 2020 16:48:48 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Matthew Wilcox <willy@...radead.org>,
        Wang Hai <wanghai38@...wei.com>
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: kobject_init_and_add is easy to misuse

On 02/06/2020 15.10, Matthew Wilcox wrote:
> On Tue, Jun 02, 2020 at 07:50:33PM +0800, Wang Hai wrote:
>> syzkaller reports for memory leak when kobject_init_and_add()
>> returns an error in the function sysfs_slab_add() [1]
>>
>> When this happened, the function kobject_put() is not called for the
>> corresponding kobject, which potentially leads to memory leak.
>>
>> This patch fixes the issue by calling kobject_put() even if
>> kobject_init_and_add() fails.
> 
> I think this speaks to a deeper problem with kobject_init_and_add()
> -- the need to call kobject_put() if it fails is not readily apparent
> to most users.  This same bug appears in the first three users of
> kobject_init_and_add() that I checked --
> arch/ia64/kernel/topology.c
> drivers/firmware/dmi-sysfs.c
> drivers/firmware/efi/esrt.c
> drivers/scsi/iscsi_boot_sysfs.c
> 
> Some do get it right --
> arch/powerpc/kernel/cacheinfo.c
> drivers/gpu/drm/ttm/ttm_bo.c
> drivers/gpu/drm/ttm/ttm_memory.c
> drivers/infiniband/hw/mlx4/sysfs.c
> 
> I'd argue that the current behaviour is wrong, that kobject_init_and_add()
> should call kobject_put() if the add fails.  This would need a tree-wide
> audit.  But somebody needs to do that anyway because based on my random
> sampling, half of the users currently get it wrong.
> 

At his point kobject doesn't own kmem-cache structure itself yet.

So calling kobject_put() will free kmem-cache and then it will be
freed second time on error path in create_cache().

I suppose freeing in case of error should be pushed from common
create_cache() into slab-specific __kmem_cache_create().