[PATCH 03/21] dmaengine: axi-dmac: Annotate struct axi_dmac_desc with __counted_by

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Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family

As found with Coccinelle[1], add __counted_by for struct axi_dmac_desc.
Additionally, since the element count member must be set before accessing
the annotated flexible array member, move its initialization earlier.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Vinod Koul <vkoul@xxxxxxxxxx>
Cc: Lars-Peter Clausen <lars@xxxxxxxxxx>
Cc: dmaengine@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
 drivers/dma/dma-axi-dmac.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/dma-axi-dmac.c b/drivers/dma/dma-axi-dmac.c
index fc7cdad37161..b9f85cb20d3e 100644
--- a/drivers/dma/dma-axi-dmac.c
+++ b/drivers/dma/dma-axi-dmac.c
@@ -117,7 +117,7 @@ struct axi_dmac_desc {
 	unsigned int num_submitted;
 	unsigned int num_completed;
 	unsigned int num_sgs;
-	struct axi_dmac_sg sg[];
+	struct axi_dmac_sg sg[] __counted_by(num_sgs);
 struct axi_dmac_chan {
@@ -484,12 +484,11 @@ static struct axi_dmac_desc *axi_dmac_alloc_desc(unsigned int num_sgs)
 	desc = kzalloc(struct_size(desc, sg, num_sgs), GFP_NOWAIT);
 	if (!desc)
 		return NULL;
+	desc->num_sgs = num_sgs;
 	for (i = 0; i < num_sgs; i++)
 		desc->sg[i].id = AXI_DMAC_SG_UNUSED;
-	desc->num_sgs = num_sgs;
 	return desc;

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