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Message-ID: <CAHk-=wjxAk=PQBX4OvscNfGKfc+M8iKmNd6D39wOZzXV0k729w@mail.gmail.com>
Date: Sat, 21 Oct 2023 11:08:31 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Vasily Gorbik <gor@...ux.ibm.com>,
Andy Shevchenko <andriy.shevchenko@...el.com>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
Kees Cook <keescook@...omium.org>
Cc: Heiko Carstens <hca@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [GIT PULL] s390 fixes for 6.6-rc7
Just re-quoting my suggestion here and adding Andy and Dmitry, who did
the original bitmap_alloc() helper interfaces a few years ago.
Also adding Kees in case he has any hardening suggestions, since this
is about (incorrect) overflow handling.
Kees: see my rant about mindlessly doing overflow handling in the wrong place in
https://lore.kernel.org/all/CAHk-=wgTUz1bdY6zvsN4ED0arCLE8Sb==1GH8d0sjm5bu7zesQ@mail.gmail.com/
in case you or somebody has a better idea for BITS_TO_LONG handling
than just "you need to check for zero before and after".
Linus
On Sat, 21 Oct 2023 at 10:56, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> If you *do* want to add proper overflow handling, you'd need to either
> fix BITS_TO_LONGS() some way (which is actually non-trivial since it
> needs to be able to stay a constant and only use the argument once),
> or you do something like
>
> if (!bits)
> return ZERO_SIZE_PTR;
> longs = BITS_TO_LONG(bits);
> if (!longs)
> return NULL;
> return vzalloc(longs * sizeof(long));
>
> and I'd suggest maybe we should
>
> (a) do the above checking in our bitmap_alloc() routines
>
> (b) also change our bitmap_alloc() routines to take 'size_t' instead
> of 'unsigned int' bit counts
>
> (c) and finally, add that vzalloc() case, but simply using
>
> kvmalloc_array(n, size, flags | __GFP_ZERO);
>
> instead.
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