Re: [PATCH] memory: gpmc: fix out of bounds read and dereference on gpmc_cs[]
From: Krzysztof Kozlowski
Date: Wed Feb 24 2021 - 03:13:24 EST
On Wed, Feb 24, 2021 at 10:55:52AM +0300, Dan Carpenter wrote:
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On Tue, Feb 23, 2021 at 07:38:21PM +0000, Colin King wrote:
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> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
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>
>
> Currently the array gpmc_cs is indexed by cs before it cs is range checked
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> and the pointer read from this out-of-index read is dereferenced. Fix this
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> by performing the range check on cs before the read and the following
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> pointer dereference.
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>
>
> Addresses-Coverity: ("Negative array index read")
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> Fixes: 186401937927 ("memory: gpmc: Move omap gpmc code to live under drivers")
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> Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>
> ---
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> drivers/memory/omap-gpmc.c | 7 +++++--
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> 1 file changed, 5 insertions(+), 2 deletions(-)
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>
>
> diff --git a/drivers/memory/omap-gpmc.c b/drivers/memory/omap-gpmc.c
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> index cfa730cfd145..f80c2ea39ca4 100644
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> --- a/drivers/memory/omap-gpmc.c
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> +++ b/drivers/memory/omap-gpmc.c
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> @@ -1009,8 +1009,8 @@ EXPORT_SYMBOL(gpmc_cs_request);
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>
>
> void gpmc_cs_free(int cs)
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> {
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> - struct gpmc_cs_data *gpmc = &gpmc_cs[cs];
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> - struct resource *res = &gpmc->mem;
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>
There is no actual dereferencing going on here, it just taking the
>
addresses. But the patch is also harmless and improves readability.
Hm, in the second line indeed the compiler will just calculate the
offset of "mem" field against the "gpmc_cs+cs" and return it's probable
address.
To me still the code is a little bit non-obvious or obfuscated - first
you play with the array[index] and then you check the validity of index.
Best regards,
Krzysztof