On Sun 27 Mar 2022 at 21:08, Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx> wrote: > On Sun, 27 Mar 2022 13:03:14 +0200, Jerome Brunet <jbrunet@xxxxxxxxxxxx> wrote: >> On Sun 27 Mar 2022 at 16:18, Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx> 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. This is a speculation which just does not hold ATM. What this patch does is adding dead code cause the last "return -EINVAL;" will never be reached. This no fix nor improvement. > 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@xxxxxxxxx/ You can make improvements as long as the code is kept clean an maintainable. Dead code is not OK.
