[PATCH 13/21] dmaengine: stm32-mdma: Annotate struct stm32_mdma_desc with __counted_by

Kees Cook
2023-08-18T00:00:09Z

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 stm32_mdma_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@kernel.org>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: dmaengine@vger.kernel.org
Cc: linux-stm32@st-md-mailman.stormreply.com
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
drivers/dma/stm32-mdma.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/stm32-mdma.c b/drivers/dma/stm32-mdma.c
index 0de234022c6d..926d6ecf1274 100644
--- a/drivers/dma/stm32-mdma.c
+++ b/drivers/dma/stm32-mdma.c
@@ -224,7 +224,7 @@ struct stm32_mdma_desc {
u32 ccr;
bool cyclic;
u32 count;
- struct stm32_mdma_desc_node node[];
+ struct stm32_mdma_desc_node node[] __counted_by(count);
};

struct stm32_mdma_dma_config {
@@ -321,6 +321,7 @@ static struct stm32_mdma_desc *stm32_mdma_alloc_desc(
desc = kzalloc(struct_size(desc, node, count), GFP_NOWAIT);
if (!desc)
return NULL;
+ desc->count = count;

for (i = 0; i < count; i++) {
desc->node[i].hwdesc =
@@ -330,8 +331,6 @@ static struct stm32_mdma_desc *stm32_mdma_alloc_desc(
goto err;
}

- desc->count = count;
-
return desc;

err:
--
2.34.1