Re: [PATCH] media: ngene: Fix out-of-bounds bug in ngene_command_config_free_buf()

[Gustavo A. R. Silva]

Hi all,

I'm taking this in my tree[1] for 5.14-rc3.

Thanks
--
Gustavo

[1] https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git/log/?h=for-next/array-bounds

On 4/21/21 12:40, Kees Cook wrote:
> On Mon, Apr 19, 2021 at 07:16:31PM -0500, Gustavo A. R. Silva wrote:
>> Fix an 11-year old bug in ngene_command_config_free_buf() while
>> addressing the following warnings caught with -Warray-bounds:
>>
>> arch/alpha/include/asm/string.h:22:16: warning: '__builtin_memcpy' offset [12, 16] from the object at 'com' is out of the bounds of referenced subobject 'config' with type 'unsigned char' at offset 10 [-Warray-bounds]
>> arch/x86/include/asm/string_32.h:182:25: warning: '__builtin_memcpy' offset [12, 16] from the object at 'com' is out of the bounds of referenced subobject 'config' with type 'unsigned char' at offset 10 [-Warray-bounds]
>>
>> The problem is that the original code is trying to copy 6 bytes of
>> data into a one-byte size member _config_ of the wrong structue
>> FW_CONFIGURE_BUFFERS, in a single call to memcpy(). This causes a
>> legitimate compiler warning because memcpy() overruns the length
>> of &com.cmd.ConfigureBuffers.config. It seems that the right
>> structure is FW_CONFIGURE_FREE_BUFFERS, instead, because it contains
>> 6 more members apart from the header _hdr_. Also, the name of
>> the function ngene_command_config_free_buf() suggests that the actual
>> intention is to ConfigureFreeBuffers, instead of ConfigureBuffers
>> (which configuration takes place in the function ngene_command_config_buf(),
>> above).
>>
>> Fix this by enclosing those 6 members of struct FW_CONFIGURE_FREE_BUFFERS
>> into new struct config, and use &com.cmd.ConfigureFreeBuffers.config as
>> the destination address, instead of &com.cmd.ConfigureBuffers.config,
>> when calling memcpy().
>>
>> This also helps with the ongoing efforts to globally enable
>> -Warray-bounds and get us closer to being able to tighten the
>> FORTIFY_SOURCE routines on memcpy().
>>
>> Link: https://github.com/KSPP/linux/issues/109
>> Fixes: dae52d009fc9 ("V4L/DVB: ngene: Initial check-in")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Reported-by: kernel test robot <lkp@xxxxxxxxx>
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> 
> Nice find! Yeah, this looks like a copy/paste bug but it went unnoticed
> because it's occupying the same memory via the union. Heh.
> 
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> 
> -Kees
> 
>> ---
>>  drivers/media/pci/ngene/ngene-core.c |  2 +-
>>  drivers/media/pci/ngene/ngene.h      | 14 ++++++++------
>>  2 files changed, 9 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/media/pci/ngene/ngene-core.c b/drivers/media/pci/ngene/ngene-core.c
>> index 07f342db6701..7481f553f959 100644
>> --- a/drivers/media/pci/ngene/ngene-core.c
>> +++ b/drivers/media/pci/ngene/ngene-core.c
>> @@ -385,7 +385,7 @@ static int ngene_command_config_free_buf(struct ngene *dev, u8 *config)
>>  
>>  	com.cmd.hdr.Opcode = CMD_CONFIGURE_FREE_BUFFER;
>>  	com.cmd.hdr.Length = 6;
>> -	memcpy(&com.cmd.ConfigureBuffers.config, config, 6);
>> +	memcpy(&com.cmd.ConfigureFreeBuffers.config, config, 6);
>>  	com.in_len = 6;
>>  	com.out_len = 0;
>>  
>> diff --git a/drivers/media/pci/ngene/ngene.h b/drivers/media/pci/ngene/ngene.h
>> index 84f04e0e0cb9..3d296f1998a1 100644
>> --- a/drivers/media/pci/ngene/ngene.h
>> +++ b/drivers/media/pci/ngene/ngene.h
>> @@ -407,12 +407,14 @@ enum _BUFFER_CONFIGS {
>>  
>>  struct FW_CONFIGURE_FREE_BUFFERS {
>>  	struct FW_HEADER hdr;
>> -	u8   UVI1_BufferLength;
>> -	u8   UVI2_BufferLength;
>> -	u8   TVO_BufferLength;
>> -	u8   AUD1_BufferLength;
>> -	u8   AUD2_BufferLength;
>> -	u8   TVA_BufferLength;
>> +	struct {
>> +		u8   UVI1_BufferLength;
>> +		u8   UVI2_BufferLength;
>> +		u8   TVO_BufferLength;
>> +		u8   AUD1_BufferLength;
>> +		u8   AUD2_BufferLength;
>> +		u8   TVA_BufferLength;
>> +	} __packed config;
>>  } __attribute__ ((__packed__));
>>  
>>  struct FW_CONFIGURE_UART {
>> -- 
>> 2.27.0
>>
>