linux-kernel - Re: [PATCH v3] misc: fastrpc: fix improper packet size calculation

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Date:   Tue, 21 Sep 2021 14:40:23 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     jeyr@...eaurora.org
Cc:     linux-arm-msm@...r.kernel.org, srinivas.kandagatla@...aro.org,
        linux-kernel@...r.kernel.org, fastrpc.upstream@....qualcomm.com
Subject: Re: [PATCH v3] misc: fastrpc: fix improper packet size calculation

On Tue, Sep 21, 2021 at 06:03:42PM +0530, jeyr@...eaurora.org wrote:
> On 2021-09-21 17:22, Greg KH wrote:
> > On Tue, Sep 21, 2021 at 05:18:15PM +0530, Jeya R wrote:
> > > The buffer list is sorted and this is not being considered while
> > > calculating packet size. This would lead to improper copy length
> > > calculation for non-dmaheap buffers which would eventually cause
> > > sending improper buffers to DSP.
> > > 
> > > Fixes: c68cfb718c8f ("misc: fastrpc: Add support for context Invoke
> > > method")
> > > Signed-off-by: Jeya R <jeyr@...eaurora.org>
> > > Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> > 
> > Does this also need to go to the stable kernels?
> Yes, this needs to go to stable kernels also as this fixes a potential issue
> which is easily reproducible.



> 
> > 
> > > ---
> > > Changes in v3:
> > > - relocate patch change list
> > > 
> > > Changes in v2:
> > > - updated commit message to proper format
> > > - added fixes tag to commit message
> > > - removed unnecessary variable initialization
> > > - removed length check during payload calculation
> > > 
> > >  drivers/misc/fastrpc.c | 10 ++++++----
> > >  1 file changed, 6 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> > > index beda610..69d45c4 100644
> > > --- a/drivers/misc/fastrpc.c
> > > +++ b/drivers/misc/fastrpc.c
> > > @@ -719,16 +719,18 @@ static int fastrpc_get_meta_size(struct
> > > fastrpc_invoke_ctx *ctx)
> > >  static u64 fastrpc_get_payload_size(struct fastrpc_invoke_ctx *ctx,
> > > int metalen)
> > >  {
> > >  	u64 size = 0;
> > > -	int i;
> > > +	int oix;
> > 
> > What does "oix" stand for?  What was wrong with i?
> It is just a general convention we use. "oix" is used to iterate through
> sorted overlap buffer list and use "i" to get corresponding unsorted list
> index. We follow the same convention at other places also, for example:
> fastrpc_get_args function.

That is the only place it is used in all of the whole kernel tree.  It
is not a normal variable for a loop, so who is "we" here?

thanks,

greg k-h