Re: [PATCH] Bluetooth: hci_core: Prefer struct_size over open coded arithmetic

[Kees Cook <keescook@chromium.org>]

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 Clang
> 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).
> 
> 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#open-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