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Date:   Wed, 21 Sep 2022 20:10:06 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Kees Cook <keescook@...omium.org>, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Alex Elder <elder@...nel.org>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian K├Ânig <christian.koenig@....com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Daniel Micay <danielmicay@...il.com>,
        Yonghong Song <yhs@...com>, Marco Elver <elver@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Jacob Shin <jacob.shin@....com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, netdev@...r.kernel.org,
        linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org, dev@...nvswitch.org,
        x86@...nel.org, linux-wireless@...r.kernel.org,
        llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: [PATCH 05/12] dma-buf: Proactively round up to kmalloc bucket size

Instead of discovering the kmalloc bucket size _after_ allocation, round
up proactively so the allocation is explicitly made for the full size,
allowing the compiler to correctly reason about the resulting size of
the buffer through the existing __alloc_size() hint.

Cc: linux-media@...r.kernel.org
Cc: dri-devel@...ts.freedesktop.org
Cc: linaro-mm-sig@...ts.linaro.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/dma-buf/dma-resv.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
index 205acb2c744d..a20f6db99b8f 100644
--- a/drivers/dma-buf/dma-resv.c
+++ b/drivers/dma-buf/dma-resv.c
@@ -98,12 +98,17 @@ static void dma_resv_list_set(struct dma_resv_list *list,
 static struct dma_resv_list *dma_resv_list_alloc(unsigned int max_fences)
 {
 	struct dma_resv_list *list;
+	size_t size = struct_size(list, table, max_fences);
 
-	list = kmalloc(struct_size(list, table, max_fences), GFP_KERNEL);
+	/* Round up to the next kmalloc bucket size. */
+	size = kmalloc_size_roundup(size);
+
+	list = kmalloc(size, GFP_KERNEL);
 	if (!list)
 		return NULL;
 
-	list->max_fences = (ksize(list) - offsetof(typeof(*list), table)) /
+	/* Given the resulting bucket size, recalculated max_fences. */
+	list->max_fences = (size - offsetof(typeof(*list), table)) /
 		sizeof(*list->table);
 
 	return list;
-- 
2.34.1

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