netdev - Re: [PATCH] bnx2: Pass allocation size to build

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Date:   Fri, 21 Oct 2022 19:06:26 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Rasesh Mody <rmody@...vell.com>, GR-Linux-NIC-Dev@...vell.com,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] bnx2: Pass allocation size to build_skb()

On Wed, Oct 19, 2022 at 05:02:55PM -0700, Jakub Kicinski wrote:
> On Tue, 18 Oct 2022 01:59:29 -0700 Kees Cook wrote:
> > In preparation for requiring that build_skb() have a non-zero size
> > argument, pass the actual data allocation size explicitly into
> > build_skb().
> 
> build_skb(, 0) has the special meaning of "head buf has been kmalloc'd",
> rather than alloc_page(). Was this changed and I missed it?

Hm, I'm not clear on it. I see ksize() being called, but I guess that
works for alloc_page() allocations too?

build_skb
	__build_skb:
		__build_skb_around:
		        unsigned int size = frag_size ? : ksize(data);

So I guess in this case, this patch is wrong, and should instead be this
to match the ksize() used in build_skb():

diff --git a/drivers/net/ethernet/broadcom/bnx2.c
b/drivers/net/ethernet/broadcom/bnx2.c
index fec57f1982c8..dbe310144780 100644
--- a/drivers/net/ethernet/broadcom/bnx2.c
+++ b/drivers/net/ethernet/broadcom/bnx2.c
@@ -5415,8 +5415,9 @@ bnx2_set_rx_ring_size(struct bnx2 *bp, u32 size)
 
        bp->rx_buf_use_size = rx_size;
        /* hw alignment + build_skb() overhead*/
-       bp->rx_buf_size = SKB_DATA_ALIGN(bp->rx_buf_use_size + BNX2_RX_ALIGN) +
-               NET_SKB_PAD + SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+       bp->rx_buf_size = kmalloc_size_roundup(
+               SKB_DATA_ALIGN(bp->rx_buf_use_size + BNX2_RX_ALIGN) +
+               NET_SKB_PAD + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)));
        bp->rx_jumbo_thresh = rx_size - BNX2_RX_OFFSET;
        bp->rx_ring_size = size;
        bp->rx_max_ring = bnx2_find_max_ring(size, BNX2_MAX_RX_RINGS);


-- 
Kees Cook