linux-kernel - Re: [PATCH] mm/slub: fix to return errno if kmalloc() fails

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Message-ID: <4b87891d-b475-0ad6-db36-a9c1f334c785@wanadoo.fr>
Date:   Tue, 13 Sep 2022 07:26:56 +0200
From:   Marion & Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Chao Yu <chao@...nel.org>,
        "Vlastimil Babka (SUSE)" <vbabka@...nel.org>, linux-mm@...ck.org
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        Chao Yu <chao.yu@...o.com>, muchun.song@...ux.dev
Subject: Re: [PATCH] mm/slub: fix to return errno if kmalloc() fails


Le 13/09/2022 à 05:42, Chao Yu a écrit :
> On 2022/9/10 0:47, Christophe JAILLET wrote:
>> Le 30/08/2022 à 16:10, Chao Yu a écrit :
>>> From: Chao Yu <chao.yu@...o.com>
>>>
>>> In create_unique_id(), kmalloc(, GFP_KERNEL) can fail due to
>>> out-of-memory, if it fails, return errno correctly rather than
>>> triggering panic via BUG_ON();
>>>
>>> kernel BUG at mm/slub.c:5893!
>>> Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
>>>
>>> Call trace:
[...]
>>>
>>> Cc: <stable@...nel.org>
>>> Reported-by: syzbot+81684812ea68216e08c5@...kaller.appspotmail.com
>>> Signed-off-by: Chao Yu <chao.yu@...o.com>
>>> ---
>>>   mm/slub.c | 5 ++++-
>>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/mm/slub.c b/mm/slub.c
>>> index 862dbd9af4f5..e6f3727b9ad2 100644
>>> --- a/mm/slub.c
>>> +++ b/mm/slub.c
>>> @@ -5890,7 +5890,8 @@ static char *create_unique_id(struct 
>>> kmem_cache *s)
>>>       char *name = kmalloc(ID_STR_LENGTH, GFP_KERNEL);
>>
>> Hi,
>>
>> looks that ID_STR_LENGTH could even be reduced to 32 or 16.
>>
>> The 2nd BUG_ON at the end of the function could certainly be just 
>> removed as well or remplaced by a:
>>         if (p > name + ID_STR_LENGTH - 1) {
>>          kfree(name);
>>          return -E<something>;
>>      }
>
> Hi Christophe, Vlastimil,
>
> Should I include this in v3? or may be in another patch?

Hi,

My own preference would be for 3 patches.

Yours, as-is.
It fixes a specific issue spotted by syzbot.

Another one for removing a BUG_ON() (that, IIUC can't happen!)
Mostly a clean-up or a good practice in order to remove BUG_ON() from 
the kernel we it can be handled another way.

Eventually a 3rd one for reducing ID_STR_LENGTH.
I guess that it is safe to reduce it to 32 or 16, but the impact on RL 
would be so small, that I wonder if it worth proposing it.

Just my 2c,

CJ



>
> Thanks,
>
>>
>> Just my 2c,
>>
>> CJ
>>
>>>       char *p = name;
>>> -    BUG_ON(!name);
>>> +    if (!name)
>>> +        return ERR_PTR(-ENOMEM);
>>>       *p++ = ':';
>>>       /*
>>> @@ -5948,6 +5949,8 @@ static int sysfs_slab_add(struct kmem_cache *s)
>>>            * for the symlinks.
>>>            */
>>>           name = create_unique_id(s);
>>> +        if (IS_ERR(name))
>>> +            return PTR_ERR(name);
>>>       }
>>>       s->kobj.kset = kset;
>>