[PATCH 18/21] dmaengine: ti: omap-dma: Annotate struct omap_desc with __counted_by

[Kees Cook]

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
functions).

As found with Coccinelle[1], add __counted_by for struct omap_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: Peter Ujfalusi <peter.ujfalusi@xxxxxxxxx>
Cc: dmaengine@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 drivers/dma/ti/omap-dma.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/ti/omap-dma.c b/drivers/dma/ti/omap-dma.c
index cf96cf915c0c..11ac3fc0a52a 100644
--- a/drivers/dma/ti/omap-dma.c
+++ b/drivers/dma/ti/omap-dma.c
@@ -124,7 +124,7 @@ struct omap_desc {
 	uint32_t csdp;		/* CSDP value */
 
 	unsigned sglen;
-	struct omap_sg sg[];
+	struct omap_sg sg[] __counted_by(sglen);
 };
 
 enum {
@@ -1005,6 +1005,7 @@ static struct dma_async_tx_descriptor *omap_dma_prep_slave_sg(
 	d = kzalloc(struct_size(d, sg, sglen), GFP_ATOMIC);
 	if (!d)
 		return NULL;
+	d->sglen = sglen;
 
 	d->dir = dir;
 	d->dev_addr = dev_addr;
@@ -1120,8 +1121,6 @@ static struct dma_async_tx_descriptor *omap_dma_prep_slave_sg(
 		}
 	}
 
-	d->sglen = sglen;
-
 	/* Release the dma_pool entries if one allocation failed */
 	if (ll_failed) {
 		for (i = 0; i < d->sglen; i++) {
-- 
2.34.1