linux-kernel - Re: [PATCH v2] mtd: Add check and kfree() for kcalloc()

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Message-ID: <f9a35a4f-b774-4480-910a-cdcf926df41b@wanadoo.fr>
Date: Tue, 4 Feb 2025 21:50:45 +0100
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Jiri Slaby <jirislaby@...nel.org>,
 Jiasheng Jiang <jiashengjiangcool@...il.com>
Cc: gmpy.liaowx@...il.com, kees@...nel.org, linux-kernel@...r.kernel.org,
 linux-mtd@...ts.infradead.org, miquel.raynal@...tlin.com, richard@....at,
 vigneshr@...com, stable@...r.kernel.org
Subject: Re: [PATCH v2] mtd: Add check and kfree() for kcalloc()

Le 04/02/2025 à 07:36, Jiri Slaby a écrit :
> On 04. 02. 25, 7:17, Christophe JAILLET wrote:
>> Le 04/02/2025 à 03:33, Jiasheng Jiang a écrit :
>>> Add a check for kcalloc() to ensure successful allocation.
>>> Moreover, add kfree() in the error-handling path to prevent memory 
>>> leaks.
>>>
>>> Fixes: 78c08247b9d3 ("mtd: Support kmsg dumper based on pstore/blk")
>>> Cc: <stable@...r.kernel.org> # v5.10+
>>> Signed-off-by: Jiasheng Jiang <jiashengjiangcool@...il.com>
>>> ---
>>> Changelog:
>>>
>>> v1 -> v2:
>>>
>>> 1. Remove redundant logging.
>>> 2. Add kfree() in the error-handling path.
>>> ---
>>>   drivers/mtd/mtdpstore.c | 19 ++++++++++++++++++-
>>>   1 file changed, 18 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/mtd/mtdpstore.c b/drivers/mtd/mtdpstore.c
>>> index 7ac8ac901306..2d8e330dd215 100644
>>> --- a/drivers/mtd/mtdpstore.c
>>> +++ b/drivers/mtd/mtdpstore.c
>>> @@ -418,10 +418,17 @@ static void mtdpstore_notify_add(struct 
>>> mtd_info *mtd)
>>>       longcnt = BITS_TO_LONGS(div_u64(mtd->size, info->kmsg_size));
>>>       cxt->rmmap = kcalloc(longcnt, sizeof(long), GFP_KERNEL);
>>> +    if (!cxt->rmmap)
>>> +        goto end;
>>
>> Nitpick: Could be a direct return.
>>
>>> +
>>>       cxt->usedmap = kcalloc(longcnt, sizeof(long), GFP_KERNEL);
>>> +    if (!cxt->usedmap)
>>> +        goto free_rmmap;
>>>       longcnt = BITS_TO_LONGS(div_u64(mtd->size, mtd->erasesize));
>>>       cxt->badmap = kcalloc(longcnt, sizeof(long), GFP_KERNEL);
>>> +    if (!cxt->badmap)
>>> +        goto free_usedmap;
>>>       /* just support dmesg right now */
>>>       cxt->dev.flags = PSTORE_FLAGS_DMESG;
>>> @@ -435,10 +442,20 @@ static void mtdpstore_notify_add(struct 
>>> mtd_info *mtd)
>>>       if (ret) {
>>>           dev_err(&mtd->dev, "mtd%d register to psblk failed\n",
>>>                   mtd->index);
>>> -        return;
>>> +        goto free_badmap;
>>>       }
>>>       cxt->mtd = mtd;
>>>       dev_info(&mtd->dev, "Attached to MTD device %d\n", mtd->index);
>>> +    goto end;
>>
>> Mater of taste, but I think that having an explicit return here would 
>> be clearer that a goto end;
> 
> Yes, drop the whole end.
> 
>>> +free_badmap:
>>> +    kfree(cxt->badmap);
>>> +free_usedmap:
>>> +    kfree(cxt->usedmap);
>>> +free_rmmap:
>>> +    kfree(cxt->rmmap);
>>
>> I think that in all these paths, you should also have
>>      cxt->XXXmap = NULL;
>> after the kfree().
>>
>> otherwise when mtdpstore_notify_remove() is called, you could have a 
>> double free.
> 
> Right, and this is already a problem for failing 
> register_pstore_device() in _add() -- there is unconditional 
> unregister_pstore_device() in _remove(). Should _remove() check cxt->mtd 
> first?

Not sure it is needed.
IIUC, [1] would not match in this case, because [2] would not have been 
executed. Agreed?

CJ


[1]: https://elixir.bootlin.com/linux/v6.13/source/fs/pstore/blk.c#L169
[2]: https://elixir.bootlin.com/linux/v6.13/source/fs/pstore/blk.c#L141

> 
> thanks,