Re: [PATCH] iio: gts-helper: Fix memory leaks in iio_gts_build_avail_scale_table()

[Matti Vaittinen]

Hi Jinjie, Jonathan,

On 12/10/2024 19:15, Jonathan Cameron wrote:
> On Fri, 11 Oct 2024 17:55:12 +0800
> Jinjie Ruan <ruanjinjie@xxxxxxxxxx> wrote:
>
> > modprobe iio-test-gts and rmmod it, then the following memory leak
> > occurs:
> >
> > 	unreferenced object 0xffffff80c810be00 (size 64):
> > 	  comm "kunit_try_catch", pid 1654, jiffies 4294913981
> > 	  hex dump (first 32 bytes):
> > 	    02 00 00 00 08 00 00 00 20 00 00 00 40 00 00 00  ........ ...@...
> > 	    80 00 00 00 00 02 00 00 00 04 00 00 00 08 00 00  ................
> > 	  backtrace (crc a63d875e):
> > 	    [<0000000028c1b3c2>] kmemleak_alloc+0x34/0x40
> > 	    [<000000001d6ecc87>] __kmalloc_noprof+0x2bc/0x3c0
> > 	    [<00000000393795c1>] devm_iio_init_iio_gts+0x4b4/0x16f4
> > 	    [<0000000071bb4b09>] 0xffffffdf052a62e0
> > 	    [<000000000315bc18>] 0xffffffdf052a6488
> > 	    [<00000000f9dc55b5>] kunit_try_run_case+0x13c/0x3ac
> > 	    [<00000000175a3fd4>] kunit_generic_run_threadfn_adapter+0x80/0xec
> > 	    [<00000000f505065d>] kthread+0x2e8/0x374
> > 	    [<00000000bbfb0e5d>] ret_from_fork+0x10/0x20
> > 	unreferenced object 0xffffff80cbfe9e70 (size 16):
> > 	  comm "kunit_try_catch", pid 1658, jiffies 4294914015
> > 	  hex dump (first 16 bytes):
> > 	    10 00 00 00 40 00 00 00 80 00 00 00 00 00 00 00  ....@...........
> > 	  backtrace (crc 857f0cb4):
> > 	    [<0000000028c1b3c2>] kmemleak_alloc+0x34/0x40
> > 	    [<000000001d6ecc87>] __kmalloc_noprof+0x2bc/0x3c0
> > 	    [<00000000393795c1>] devm_iio_init_iio_gts+0x4b4/0x16f4
> > 	    [<0000000071bb4b09>] 0xffffffdf052a62e0
> > 	    [<000000007d089d45>] 0xffffffdf052a6864
> > 	    [<00000000f9dc55b5>] kunit_try_run_case+0x13c/0x3ac
> > 	    [<00000000175a3fd4>] kunit_generic_run_threadfn_adapter+0x80/0xec
> > 	    [<00000000f505065d>] kthread+0x2e8/0x374
> > 	    [<00000000bbfb0e5d>] ret_from_fork+0x10/0x20
> > 	......
> >
> > It includes 5*5 times "size 64" memory leaks, which correspond to 5 times
> > test_init_iio_gain_scale() calls with gts_test_gains size 10 (10*size(int))
> > and gts_test_itimes size 5. It also includes 5*1 times "size 16"
> > memory leak, which correspond to one time __test_init_iio_gain_scale()
> > call with gts_test_gains_gain_low size 3 (3*size(int)) and gts_test_itimes
> > size 5.
> >
> > The reason is that the per_time_gains[i] is not freed which is allocated in
> > the "gts->num_itime" for loop in iio_gts_build_avail_scale_table().
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Fixes: 38416c28e168 ("iio: light: Add gain-time-scale helpers")
> > Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
> Hi Jinjie,
>
> Your explanation looks correct to me.  I'll wait a while though to give Matti time
> to take a look as well.

Sorry for late reply - I spent last couple of days walking through the 
swamps and forests in the wilderness.

Something was bothering me with this. I browsed through the code and all 
the allocations and I'm not able to see why these arrays shouldn't be 
freed. I did even go through the versions I've sent on list trying to 
find out what bothers me.

Well, I found nothing. The version 2 had some code which looped through 
these arrays freeing them - in an error path - but not in successful 
case. It seemed as if I had thought these values had to be maintained - 
but I really can't see why.

So - thanks. I suppose leaving the memory not freed is just a bug :) 
Nice that you killed this one :)

Reviewed-by: Matti Vaittinen <mazziesaccount@xxxxxxxxx>

> Thanks,
>
> Jonathan
>
> > ---
> >   drivers/iio/industrialio-gts-helper.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/iio/industrialio-gts-helper.c b/drivers/iio/industrialio-gts-helper.c
> > index 59d7615c0f56..7326c7949244 100644
> > --- a/drivers/iio/industrialio-gts-helper.c
> > +++ b/drivers/iio/industrialio-gts-helper.c
> > @@ -307,6 +307,8 @@ static int iio_gts_build_avail_scale_table(struct iio_gts *gts)
> >   	if (ret)
> >   		goto err_free_out;
> >   
> > +	for (i = 0; i < gts->num_itime; i++)
> > +		kfree(per_time_gains[i]);
> >   	kfree(per_time_gains);
> >   	gts->per_time_avail_scale_tables = per_time_scales;
> >