RE: [PATCH v2 06/16] igb: Proactively round up to kmalloc bucket size

From: "Ruhl, Michael J" <michael.j.ruhl@intel.com>
To: Kees Cook <keescook@chromium.org>, Vlastimil Babka <vbabka@suse.cz>
Cc: "Brandeburg, Jesse" <jesse.brandeburg@intel.com>,
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Subject: RE: [PATCH v2 06/16] igb: Proactively round up to kmalloc bucket size
Date: Mon, 26 Sep 2022 15:49:02 +0000	[thread overview]
Message-ID: <DM5PR11MB13241141BB4C863F1A01D958C1529@DM5PR11MB1324.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20220923202822.2667581-7-keescook@chromium.org>

>-----Original Message-----
>From: Kees Cook <keescook@chromium.org>
>Sent: Friday, September 23, 2022 4:28 PM
>To: Vlastimil Babka <vbabka@suse.cz>
>Cc: Kees Cook <keescook@chromium.org>; Brandeburg, Jesse
><jesse.brandeburg@intel.com>; Nguyen, Anthony L
><anthony.l.nguyen@intel.com>; David S. Miller <davem@davemloft.net>;
>Eric Dumazet <edumazet@google.com>; Jakub Kicinski <kuba@kernel.org>;
>Paolo Abeni <pabeni@redhat.com>; intel-wired-lan@lists.osuosl.org;
>netdev@vger.kernel.org; Ruhl, Michael J <michael.j.ruhl@intel.com>;
>Hyeonggon Yoo <42.hyeyoo@gmail.com>; Christoph Lameter
><cl@linux.com>; Pekka Enberg <penberg@kernel.org>; David Rientjes
><rientjes@google.com>; Joonsoo Kim <iamjoonsoo.kim@lge.com>; Andrew
>Morton <akpm@linux-foundation.org>; Greg Kroah-Hartman
><gregkh@linuxfoundation.org>; Nick Desaulniers
><ndesaulniers@google.com>; Alex Elder <elder@kernel.org>; Josef Bacik
><josef@toxicpanda.com>; David Sterba <dsterba@suse.com>; Sumit Semwal
><sumit.semwal@linaro.org>; Christian König <christian.koenig@amd.com>;
>Daniel Micay <danielmicay@gmail.com>; Yonghong Song <yhs@fb.com>;
>Marco Elver <elver@google.com>; Miguel Ojeda <ojeda@kernel.org>; linux-
>kernel@vger.kernel.org; linux-mm@kvack.org; linux-btrfs@vger.kernel.org;
>linux-media@vger.kernel.org; dri-devel@lists.freedesktop.org; linaro-mm-
>sig@lists.linaro.org; linux-fsdevel@vger.kernel.org; dev@openvswitch.org;
>x86@kernel.org; llvm@lists.linux.dev; linux-hardening@vger.kernel.org
>Subject: [PATCH v2 06/16] igb: Proactively round up to kmalloc bucket size
>
>In preparation for removing the "silently change allocation size"
>users of ksize(), explicitly round up all q_vector allocations so that
>allocations can be correctly compared to ksize().
>
>Additionally fix potential use-after-free in the case of new allocation
>failure: only free memory if the replacement allocation succeeds.
>
>Cc: Jesse Brandeburg <jesse.brandeburg@intel.com>
>Cc: Tony Nguyen <anthony.l.nguyen@intel.com>
>Cc: "David S. Miller" <davem@davemloft.net>
>Cc: Eric Dumazet <edumazet@google.com>
>Cc: Jakub Kicinski <kuba@kernel.org>
>Cc: Paolo Abeni <pabeni@redhat.com>
>Cc: intel-wired-lan@lists.osuosl.org
>Cc: netdev@vger.kernel.org
>Signed-off-by: Kees Cook <keescook@chromium.org>
>---
> drivers/net/ethernet/intel/igb/igb_main.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/net/ethernet/intel/igb/igb_main.c
>b/drivers/net/ethernet/intel/igb/igb_main.c
>index 2796e81d2726..eb51e531c096 100644
>--- a/drivers/net/ethernet/intel/igb/igb_main.c
>+++ b/drivers/net/ethernet/intel/igb/igb_main.c
>@@ -1195,15 +1195,16 @@ static int igb_alloc_q_vector(struct igb_adapter
>*adapter,
> 		return -ENOMEM;
>
> 	ring_count = txr_count + rxr_count;
>-	size = struct_size(q_vector, ring, ring_count);
>+	size = kmalloc_size_roundup(struct_size(q_vector, ring, ring_count));

This looks good to me...

> 	/* allocate q_vector and rings */
> 	q_vector = adapter->q_vector[v_idx];
> 	if (!q_vector) {
> 		q_vector = kzalloc(size, GFP_KERNEL);
> 	} else if (size > ksize(q_vector)) {
>-		kfree_rcu(q_vector, rcu);
> 		q_vector = kzalloc(size, GFP_KERNEL);
>+		if (q_vector)
>+			kfree_rcu(q_vector, rcu);

Even though this is in the ksize part, this seems like an unrelated change?
 Should this be in a different patch?

Also, the kfree_rcu will free q_vector after the RCU grace period?

Is that what you want to do?

How does rcu distinguish between the original q_vector, and the newly kzalloced one?

Thanks,

Mike

> 	} else {
> 		memset(q_vector, 0, size);
> 	}
>--
>2.34.1