Re: [PATCH v2 net-next 1/2] net: dsa: lan9303: Add port_fast_age and port_fdb_dump methods

Den 19. okt. 2017 17:42, skrev Egil Hjelmeland:

On 19. okt. 2017 17:15, David Laight wrote:

quoted

From: Andrew Lunn

quoted

Sent: 19 October 2017 15:15

quoted

quoted

+/* Clear learned (non-static) entry on given port */
+static void alr_loop_cb_del_port_learned(struct lan9303 *chip, u32 
dat0,
+                     u32 dat1, int portmap, void *ctx)
+{
+    int *port = ctx;

You can get the value directly to make the line below more readable:

     int port = *(int *)ctx;

You have to be a bit careful with this. You often see people
submitting patches taking away casts for void * pointers.
If they do that here, it should at least not compile...

So maybe do it in two steps?

    int * pport = ctx;
    int port = *pport;

IMHO it is best to define a struct for the 'ctx and then do:
    ..., void *v_ctx)
{
    foo_ctx *ctx = v_ctx;
    int port = ctx->port;

That stops anyone having to double-check that the *(int *)
is operating on a pointer to an integer of the correct size.

Does casting to a struct pointer require less manual double-check than
to a int-pointer? In neither cases the compiler can protect us, IFAIK.
But on the other hand, a the text "foo_ctx" can searched in the editor.
So in that respect it can somewhat aid to the double-checking.

So I can do that.

I understand now that the caller side (lan9303_port_fast_age) is
vulnerable. Say somebody has the idea to change the "port" param
of .port_fast_age from int to u8, then my code is a trap.

Thanks for the education.

Egil