linux-kernel - Re: [Nouveau] [PATCH] drm/nouveau: fix pramdac

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Date:	Wed, 17 Feb 2010 19:36:06 +0100
From:	Francisco Jerez <currojerez@...eup.net>
To:	Marcin Slusarz <marcin.slusarz@...il.com>
Cc:	nouveau@...ts.freedesktop.org, kernel-janitors@...r.kernel.org,
	Dan Carpenter <error27@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [Nouveau] [PATCH] drm/nouveau: fix pramdac_table range checking

Marcin Slusarz <marcin.slusarz@...il.com> writes:

> On Mon, Feb 15, 2010 at 03:40:56PM +0300, Dan Carpenter wrote:
>> This is the results from:
>>     make C=1 CHECK="/path/to/smatch -p=kernel" bzImage modules | tee warns.txt
>>     grep -w overflow warns.txt | uniq -f 3 | tee err-list
>> 
>> I hacked on the buffer overflow check last weekend and these are the 
>> results.  It has way more false positives than the other bug lists 
>> I've posted, but it's still kinda neat.
>> 
>> It works like this:
>> 
>> lib/zlib_inflate/inftrees.c
>>    112      for (min = 1; min <= MAXBITS; min++)
>>    113          if (count[min] != 0) break;
>>    114      if (root < min) root = min;
>> smatch thinks "min" can be MAXBITS here.
>> 
>> One bad thing is that if you have code like:
>>         if (foo == 42)
>> 		frob();
>> Smatch thinks that "foo" can be 43 after the if statement.
>> 
>> The format is:
>> file.c +<line> function(<lines into function>) warning 'array_name' <array size> <= <offset>
>> 
>> regards,
>> dan carpenter
>> 
>> Previous bug lists:
>> * Putting too much data on the stack
>>   http://lkml.indiana.edu/hypermail/linux/kernel/1002.1/01252.html
>> 
>> * Assigning negative values to unsigned variables
>>   http://lkml.indiana.edu/hypermail/linux/kernel/1001.3/01222.html
>> 
>> * Doing dma on the stack
>>   http://lkml.indiana.edu/hypermail/linux/kernel/1001.3/01231.html
>> 
>> * Dereferencing variables before verifying they are not null
>>   http://lkml.indiana.edu/hypermail/linux/kernel/1001.3/01980.html
>> 
>> (...)
>> drivers/gpu/drm/nouveau/nouveau_bios.c +770 get_tmds_index_reg(36) error: buffer overflow 'pramdac_table' 4 <= 4
>> (...)
>
> ---
> From: Marcin Slusarz <marcin.slusarz@...il.com>
> Subject: [PATCH] drm/nouveau: fix pramdac_table range checking
>
> get_tmds_index_reg reads some value from stack when mlv happens
> to be equal to size of pramdac_table array. Fix it.
>
> Reported-by: Dan Carpenter <error27@...il.com>
> Signed-off-by: Marcin Slusarz <marcin.slusarz@...il.com>
> ---
>  drivers/gpu/drm/nouveau/nouveau_bios.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_bios.c b/drivers/gpu/drm/nouveau/nouveau_bios.c
> index 2cd0fad..e7be506 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_bios.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_bios.c
> @@ -762,7 +762,7 @@ static uint32_t get_tmds_index_reg(struct drm_device *dev, uint8_t mlv)
>  			dacoffset ^= 8;
>  		return 0x6808b0 + dacoffset;
>  	} else {
> -		if (mlv > ARRAY_SIZE(pramdac_table)) {
> +		if (mlv >= ARRAY_SIZE(pramdac_table)) {
>  			NV_ERROR(dev, "Magic Lookup Value too big (%02X)\n",
>  									mlv);
>  			return 0;

Thanks. I've pushed all the three patches.


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