netdev - RE: [PATCH net-next] qed: Prevent stack corruption on MFW interaction

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Date:   Mon, 7 Nov 2016 12:25:42 +0000
From:   "Mintz, Yuval" <Yuval.Mintz@...ium.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH net-next] qed: Prevent stack corruption on MFW interaction

> > Driver uses a union for copying data to & from management firmware
> > when interacting with it.
> > Problem is that the function always copies sizeof(union) while commit
> > 2edbff8dcb5d ("qed: Learn resources from management firmware") is
> > casting a union elements which is of smaller size [24-byte instead of 88-bytes].
> >
> > Also, the union contains some inappropriate elements which increase
> > its size [should have been 32-bytes]. While this shouldn't corrupt
> > other PF messages to the MFW [as management firmware enforces
> > permissions so that each PF is allowed to write only to its own
> > mailbox] we fix this here as well.
> ...
> 
> Is it worth adding a compile-time assert on the size of the union?
> 
> 	David

I don't think so; The MFW team defines the elements and already enforces that.

It was simply a slip in my initial submission, where I omitted some
stuff that was already part of their HSI and wasn't required for that
submission, and missed the fact it was a union and not a struct
[hence uniting the removed fields to retain 'correct offsets' of fields].