linux-kernel - Re: [PATCH] mtd: nand: fix NULL pointer dereference in of_get_nand_ecc

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Message-ID: <20160426205344.17ab81cb@bbrezillon>
Date:	Tue, 26 Apr 2016 20:53:44 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Rafał Miłecki <zajec5@...il.com>
Cc:	linux-mtd@...ts.infradead.org, Richard Weinberger <richard@....at>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	linux-kernel@...r.kernel.org (open list)
Subject: Re: [PATCH] mtd: nand: fix NULL pointer dereference in
 of_get_nand_ecc_algo

On Tue, 26 Apr 2016 20:36:16 +0200
Rafał Miłecki <zajec5@...il.com> wrote:

> Our array nand_ecc_algos doesn't specify mappings for all available
> enum nand_ecc_algo values. The one missing there is NAND_ECC_UNKNOWN
> as this value is reserved for algorithm not being specified at all.
> It means we have to be careful when iterating this array and handle
> NULL values.
> 
> Signed-off-by: Rafał Miłecki <zajec5@...il.com>
> ---
> Hi Boris,
> 
> Sorry for this crash in nand subsystem :( If you think it's OK you may
> pick this patch as a fixup for
> c6e002a7ca9f ("mtd: nand: add support for "nand-ecc-algo" DT property")
> ---
>  drivers/mtd/nand/nand_base.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> index a5417a0..0eaa9dc 100644
> --- a/drivers/mtd/nand/nand_base.c
> +++ b/drivers/mtd/nand/nand_base.c
> @@ -4016,6 +4016,8 @@ static int of_get_nand_ecc_algo(struct device_node *np)
>  	err = of_property_read_string(np, "nand-ecc-algo", &pm);
>  	if (!err) {
>  		for (i = 0; i < ARRAY_SIZE(nand_ecc_algos); i++)
> +			if (!nand_ecc_algos[i])
> +				continue;

Can we add an "unknown" entry, or start iterating at NAND_ECC_HAMMING
or NAND_ECC_UNKNOWN + 1 instead of adding this extra test?

BTW, since the original commit has been applied recently I'll squash the
changes into the previous commit and rebase my branch instead of adding
a new patch (I hate breaking bisectability).


-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com