[PATCH net-next 00/15] net: Remove use of list iterator after loop body

Jakob Koschel
2022-04-07T10:32:20Z

When the list iterator loop does not exit early the list iterator variable
contains a type-confused pointer to a 'bogus' list element computed based
on the head [1].

Often a 'found' variable is used to ensure the list iterator
variable is only accessed after the loop body if the loop did exit early
(using a break or goto).

In other cases that list iterator variable is used in
combination to access the list member which reverses the invocation of
container_of() and brings back a "safe" pointer to the head of the list.

Since, due to this code patten, there were quite a few bugs discovered [2],
Linus concluded that the rule should be to never use the list iterator
after the loop and introduce a dedicated pointer for that [3].

With the new gnu11 standard, it will now be possible to limit the scope
of the list iterator variable to the traversal loop itself by defining
the variable within the for loop.
This, however, requires to remove all uses of the list iterator after
the loop.

Based on input from Paolo Abeni [4], Vinicius Costa Gomes [5], and
Jakub Kicinski [6], I've splitted all the net-next related changes into
two patch sets, where this is part 1.

Link: https://lwn.net/Articles/887097/ [1]
Link: https://lore.kernel.org/linux-kernel/20220217184829.1991035-4-jakobkoschel@gmail.com/ [2]
Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [3]
Link: https://lore.kernel.org/linux-kernel/7393b673c626fd75f2b4f8509faa5459254fb87c.camel@redhat.com/ [4]
Link: https://lore.kernel.org/linux-kernel/877d8a3sww.fsf@intel.com/ [5]
Link: https://lore.kernel.org/linux-kernel/20220403205502.1b34415d@kernel.org/ [6]