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Date: Sat, 12 Jan 2019 01:34:42 -0600
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Dan Carpenter <dan.carpenter@oracle.com>
Subject: Re: [PATCH] powerpc/powernv/npu: Allocate enough memory in
 pnv_try_setup_npu_table_group()
Message-ID: <20190112073441.GJ14180@gate.crashing.org>
References: <20190109102328.GB5476@kadam> <20190112003035.GA10427@350D>
 <20190112054426.GF1743@kadam>
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Cc: Alexey Kardashevskiy <aik@ozlabs.ru>,
 Alistair Popple <alistair@popple.id.au>,
 Mark Hairgrove <mhairgrove@nvidia.com>, kernel-janitors@vger.kernel.org,
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On Sat, Jan 12, 2019 at 08:44:26AM +0300, Dan Carpenter wrote:
> On Sat, Jan 12, 2019 at 11:30:35AM +1100, Balbir Singh wrote:
> > On Wed, Jan 09, 2019 at 01:23:29PM +0300, Dan Carpenter wrote:
> > > There is a typo so we accidentally allocate enough memory for a pointer
> > > when we wanted to allocate enough for a struct.
> > > 
> > > Fixes: 0bd971676e68 ("powerpc/powernv/npu: Add compound IOMMU groups")
> > > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > > ---
> > >  arch/powerpc/platforms/powernv/npu-dma.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/powerpc/platforms/powernv/npu-dma.c b/arch/powerpc/platforms/powernv/npu-dma.c
> > > index d7f742ed48ba..3f58c7dbd581 100644
> > > --- a/arch/powerpc/platforms/powernv/npu-dma.c
> > > +++ b/arch/powerpc/platforms/powernv/npu-dma.c
> > > @@ -564,7 +564,7 @@ struct iommu_table_group *pnv_try_setup_npu_table_group(struct pnv_ioda_pe *pe)
> > >  		}
> > >  	} else {
> > >  		/* Create a group for 1 GPU and attached NPUs for POWER8 */
> > > -		pe->npucomp = kzalloc(sizeof(pe->npucomp), GFP_KERNEL);
> > > +		pe->npucomp = kzalloc(sizeof(*pe->npucomp), GFP_KERNEL);
> > 
> > To avoid these in the future, I wonder if instead of sizeof(pe->npucomp), we insist on
> > sizeof structure
> > 
> > pe->npucomp = kzalloc(sizeof(struct npucomp), GFP_KERNEL);
> > 
> 
> The latest kernel fashion is sizeof(*ptr).  It can go wrong either way.
> I don't have strong feelings about it.  These sorts of bugs don't last
> long because they're caught in testing or with static analysis.

And it is easy to see someone forgot the * in "sizeof *ptr", and with
experience it will just automatically look wrong if it is forgotten; but
it isn't obvious at all if the wrong struct is used, which cannot happen
with the *ptr form, but happens frequently with the "sizeof(struct x)"
form.


Segher