linux-kernel - Re: [PATCH][next] afs: Use array3_size() helper in afs_extract_to

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Message-ID: <761787.1592269747@warthog.procyon.org.uk>
Date:   Tue, 16 Jun 2020 02:09:07 +0100
From:   David Howells <dhowells@...hat.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     dhowells@...hat.com, linux-afs@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH][next] afs: Use array3_size() helper in afs_extract_to_buf()

Gustavo A. R. Silva <gustavoars@...nel.org> wrote:

> Use array3_size() helper instead of the open-coded version in
> afs_extract_to_buf(). These sorts of multiplication factors need
> to be wrapped in array3_size().

For afs_deliver_cb_callback(), this adds redundant checking, as does the one
on the kmalloc() on the preceding line:

		call->buffer = kmalloc(array3_size(call->count, 3, 4),
				       GFP_KERNEL);
		if (!call->buffer)
			return -ENOMEM;

because directly above them is a range check:

		if (call->count > AFSCBMAX)
			return afs_protocol_error(call, afs_eproto_cb_fid_count);

limiting the array size to 50.

Further, note that it's *not* a 3D array.  3 * 4 is the element size and is
constant.  I've written it that way as the block is 3 XDR units, but the block
size is actually 12 bytes.

The one in the kmalloc() should also not be using array3_size() for the same
reason.

David