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

[Kees Cook <keescook@chromium.org>]

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