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

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Message-ID: <48ad8f05-a90b-499d-9e73-8e5ff032824a@kernel.org>
Date: Tue, 4 Feb 2025 07:36:14 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>,
 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()

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?

thanks,
-- 
js
suse labs