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

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Message-ID: <CANeGvZUzHVnQdwTkam4HE9EVfEf8xY4L7Y20vj5v_N-vbD9kzQ@mail.gmail.com>
Date: Tue, 4 Feb 2025 21:35:21 -0500
From: Jiasheng Jiang <jiashengjiangcool@...il.com>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc: Jiri Slaby <jirislaby@...nel.org>, 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()

Hi Christophe,

On Tue, Feb 4, 2025 at 3:50 PM Christophe JAILLET
<christophe.jaillet@...adoo.fr> wrote:
>
> 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?

Thanks for your advice.
I have submitted a v3 to replace kcalloc() with devm_kcalloc() to
prevent memory leaks.
Moreover, I moved the return value check to another patch, so that
each patch does only one thing.

-Jiasheng

>
> 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,
>