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 <202405122008.8A333C2@keescook>
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From: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date: Mon, 13 May 2024 12:31:29 -0400
Message-ID: <CABBYNZJcg5SpO_pew6ZwN98n1sR7kNZs6VtkFToyOs9NM1bO8Q@mail.gmail.com>
Subject: Re: [PATCH] Bluetooth: hci_core: Prefer struct_size over open coded arithmetic
To: Kees Cook <keescook@chromium.org>
Cc: Erick Archer <erick.archer@outlook.com>, Marcel Holtmann <marcel@holtmann.org>, 
	Johan Hedberg <johan.hedberg@gmail.com>, "David S. Miller" <davem@davemloft.net>, 
	Eric Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>, 
	"Gustavo A. R. Silva" <gustavoars@kernel.org>, Nathan Chancellor <nathan@kernel.org>, 
	Nick Desaulniers <ndesaulniers@google.com>, Bill Wendling <morbo@google.com>, 
	Justin Stitt <justinstitt@google.com>, linux-bluetooth@vger.kernel.org, 
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-hardening@vger.kernel.org, llvm@lists.linux.dev
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Hi Eric,

On Sun, May 12, 2024 at 11:08=E2=80=AFPM Kees Cook <keescook@chromium.org> =
wrote:
>
> On Sun, May 12, 2024 at 04:17:06PM +0200, Erick Archer wrote:
> > This is an effort to get rid of all multiplications from allocation
> > functions in order to prevent integer overflows [1][2].
> >
> > As the "dl" variable is a pointer to "struct hci_dev_list_req" and this
> > structure ends in a flexible array:
> >
> > struct hci_dev_list_req {
> >       [...]
> >       struct hci_dev_req dev_req[];   /* hci_dev_req structures */
> > };
> >
> > the preferred way in the kernel is to use the struct_size() helper to
> > do the arithmetic instead of the calculation "size + count * size" in
> > the kzalloc() and copy_to_user() functions.
> >
> > At the same time, prepare for the coming implementation by GCC and Clan=
g
> > of the __counted_by attribute. Flexible array members annotated with
> > __counted_by can have their accesses bounds-checked at run-time via
> > CONFIG_UBSAN_BOUNDS (for array indexing) and CONFIG_FORTIFY_SOURCE (for
> > strcpy/memcpy-family functions).
> >
> > In this case, it is important to note that the logic needs a little
> > refactoring to ensure that the "dev_num" member is initialized before
> > the first access to the flex array. Specifically, add the assignment
> > before the list_for_each_entry() loop.
> >
> > Also remove the "size" variable as it is no longer needed and refactor
> > the list_for_each_entry() loop to use dr[n] instead of (dr + n).

Have the change above split on its own patch.

> > This way, the code is more readable, idiomatic and safer.
> >
> > This code was detected with the help of Coccinelle, and audited and
> > modified manually.
> >
> > Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#op=
en-coded-arithmetic-in-allocator-arguments [1]
> > Link: https://github.com/KSPP/linux/issues/160 [2]
> >
> > Signed-off-by: Erick Archer <erick.archer@outlook.com>
>
> Looks right to me. Thanks!
>
> Reviewed-by: Kees Cook <keescook@chromium.org>
>
> --
> Kees Cook


--=20
Luiz Augusto von Dentz