Re: [PATCH] net: prestera: Add flex arrays to some structs

On Sun, May 12, 2024 at 06:10:27PM +0200, Erick Archer wrote:

The "struct prestera_msg_vtcam_rule_add_req" uses a dynamically sized
set of trailing elements. Specifically, it uses an array of structures
of type "prestera_msg_acl_action actions_msg".

The "struct prestera_msg_flood_domain_ports_set_req" also uses a
dynamically sized set of trailing elements. Specifically, it uses an
array of structures of type "prestera_msg_acl_action actions_msg".

So, use the preferred way in the kernel declaring flexible arrays [1].

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 attribute used is specifically __counted_by_le since the
counters are of type __le32.

The logic does not need to change since the counters for the flexible
arrays are asigned before any access to the arrays.

The order in which the structure prestera_msg_vtcam_rule_add_req and the
structure prestera_msg_flood_domain_ports_set_req are defined must be
changed to avoid incomplete type errors.

Also, avoid the open-coded arithmetic in memory allocator functions [2]
using the "struct_size" macro.

Moreover, the new structure members also allow us to avoid the open-
coded arithmetic on pointers. So, take advantage of this refactoring
accordingly.

This code was detected with the help of Coccinelle, and audited and
modified manually.

Link: https://www.kernel.org/doc/html/next/process/deprecated.html#zero-length-and-one-element-arrays [1]
Link: https://www.kernel.org/doc/html/next/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [2]
Signed-off-by: Erick Archer <redacted>

Reviewed-by: Simon Horman <horms@kernel.org>