dmaengine: moxart-dma: Annotate struct moxart_desc with __counted_by

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 moxart_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: dmaengine@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20230817235859.49846-6-keescook@chromium.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>

diff --git a/drivers/dma/moxart-dma.c b/drivers/dma/moxart-dma.c
index a03953b3016bbb601d6259d259b05ceaaeccafc6..c48d68cbff9232acf30e4eebce051145009b25b1 100644 (file)
--- a/drivers/dma/moxart-dma.c
+++ b/drivers/dma/moxart-dma.c
@@ -124,7 +124,7 @@ struct moxart_desc {
        unsigned int                    dma_cycles;
        struct virt_dma_desc            vd;
        uint8_t                         es;
-       struct moxart_sg                sg[];
+       struct moxart_sg                sg[] __counted_by(sglen);
 };
 
 struct moxart_chan {
@@ -309,6 +309,7 @@ static struct dma_async_tx_descriptor *moxart_prep_slave_sg(
        d = kzalloc(struct_size(d, sg, sg_len), GFP_ATOMIC);
        if (!d)
                return NULL;
+       d->sglen = sg_len;
 
        d->dma_dir = dir;
        d->dev_addr = dev_addr;
@@ -319,8 +320,6 @@ static struct dma_async_tx_descriptor *moxart_prep_slave_sg(
                d->sg[i].len = sg_dma_len(sgent);
        }
 
-       d->sglen = sg_len;
-
        ch->error = 0;
 
        return vchan_tx_prep(&ch->vc, &d->vd, tx_flags);