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

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Date:   Tue, 21 Sep 2021 18:43:44 +0530
From:   jeyr@...eaurora.org
To:     Greg KH <gregkh@...uxfoundation.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 2021-09-21 18:10, Greg KH wrote:
> 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?
The convention was followed for the same file(fastrpc.c). As part of 
fastrpc_get_args
function, while iterating through sorted buffer list, oix is used as 
index and to
get unsorted index "raix", it is using "i". Just following the same way 
here to
have better understanding. Please let me know if this is a concern, it 
can be updated
to "i", "j" etc.

-- Thanks
> 
> thanks,
> 
> greg k-h