Messages in this thread | | | From | Xiaomeng Tong <> | Subject | Re: [PATCH] soc: meson: fix a missing check on list iterator | Date | Sun, 27 Mar 2022 21:08:01 +0800 |
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On Sun, 27 Mar 2022 13:03:14 +0200, Jerome Brunet <jbrunet@baylibre.com> wrote: > On Sun 27 Mar 2022 at 16:18, Xiaomeng Tong <xiam0nd.tong@gmail.com> wrote: > > > The bug is here: > > *dai_name = dai->driver->name; > > > > For for_each_component_dais(), just like list_for_each_entry, > > the list iterator 'runtime' will point to a bogus position > > containing HEAD if the list is empty or no element is found. > > This case must be checked before any use of the iterator, > > otherwise it will lead to a invalid memory access. > > > > To fix the bug, just move the assignment into loop and return > > 0 when element is found, otherwise return -EINVAL; > > Except we already checked that the id is valid and know an element will > be be found once we enter the loop. No bug here and this patch does not > seem necessary to me.
Yea, you should be right, it is not a bug here. id already be checked before enter the loop:
if (id < 0 || id >= component->num_dai) return -EINVAL;
but if component->num_dai is not correct due to miscaculation or others reason and the door is reopened, this patch can avoid a invalid memory access. Anyway, it is a good choice to use the list iterator only inside the loop, as linus suggested[1]. and we are on the way to change all these use-after-iter cases.
[1]https://lore.kernel.org/lkml/20220217184829.1991035-1-jakobkoschel@gmail.com/
-- Xiaomeng Tong
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