On Sun, May 12, 2024 at 01:17:24PM +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 rfcomm_dev_list_req" and
> this structure ends in a flexible array:
>
> struct rfcomm_dev_list_req {
> [...]
> struct rfcomm_dev_info dev_info[];
> };
>
> 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 di[n] instead of (di + 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@xxxxxxxxxxx>
Looks good!
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> [...]
> - bacpy(&(di + n)->src, &dev->src);
> - bacpy(&(di + n)->dst, &dev->dst);
> + bacpy(&di[n].src, &dev->src);
> + bacpy(&di[n].dst, &dev->dst);
Not an issue with your patch, but this helper is really pointless in the
Bluetooth tree:
static inline void bacpy(bdaddr_t *dst, const bdaddr_t *src)
{
memcpy(dst, src, sizeof(bdaddr_t));
}
So the above could just be:
di[n].src = dev->src;
di[n].dst = dev->dst;
:P
-Kees
--
Kees Cook
