Re: [PATCH] stm class: Fix out of bound access from bitmap allocation

[Sai Prakash Ranjan]

On 4/16/2019 8:30 PM, Alexander Shishkin wrote:
> Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx> writes:
>
> > From: Mulu He <muluhe@xxxxxxxxxxxxxx>
> >
> > Bitmap allocation works on array of unsigned longs and
> > for stm master allocation when the number of software
> > channels is 32, 4 bytes are allocated and there is a out of
> > bound access at the first 8 bytes access of bitmap region.
>
> Does the below fix the problem for you?
>
>  From fb22b9ab109b332e58d72df13563e270befbd0e3 Mon Sep 17 00:00:00 2001
> From: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> Date: Tue, 16 Apr 2019 17:47:02 +0300
> Subject: [PATCH] stm class: Fix channel bitmap on 32-bit systems
>
> Commit 7bd1d4093c2f ("stm class: Introduce an abstraction for System Trace
> Module devices") naively calculates the channel bitmap size in 64-bit
> chunks regardless of the size of underlying unsigned long, making the
> bitmap half as big on a 32-bit system. This leads to an out of bounds
> access with the upper half of the bitmap.
>
> Fix this by using BITS_TO_LONGS. While at it, convert to using
> struct_size() for the total size calculation of the master struct.
>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> Fixes: 7bd1d4093c2f ("stm class: Introduce an abstraction for System Trace Module devices")
> Reported-by: Mulu He <muluhe@xxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v4.4+
> ---
>   drivers/hwtracing/stm/core.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
> index 5b5807cbcf7c..8c45e79e47db 100644
> --- a/drivers/hwtracing/stm/core.c
> +++ b/drivers/hwtracing/stm/core.c
> @@ -166,11 +166,9 @@ stm_master(struct stm_device *stm, unsigned int idx)
>   static int stp_master_alloc(struct stm_device *stm, unsigned int idx)
>   {
>   	struct stp_master *master;
> -	size_t size;
>   
> -	size = ALIGN(stm->data->sw_nchannels, 8) / 8;
> -	size += sizeof(struct stp_master);
> -	master = kzalloc(size, GFP_ATOMIC);
> +	master = kzalloc(struct_size(master, chan_map, BITS_TO_LONGS(stm->data->sw_nchannels)),
> +			 GFP_ATOMIC);
>   	if (!master)
>   		return -ENOMEM;
>   

++ David

Yes it does fix the issue. Actually initial fix internally was using
BITS_TO_LONGS, don't no why they deferred from it.

Anyways thanks for the patch.

- Sai

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