linux-hardening - [PATCH] dmaengine: dw-axi-dmac: Do not dereference NULL structure

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Date:   Fri, 27 Jan 2023 14:36:27 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
Cc:     Kees Cook <keescook@...omium.org>, Vinod Koul <vkoul@...nel.org>,
        dmaengine@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sia Jee Heng <jee.heng.sia@...el.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] dmaengine: dw-axi-dmac: Do not dereference NULL structure

If "vdesc" is NULL, it cannot be used with vd_to_axi_desc(). Leave
"bytes" unchanged at 0. Seen under GCC 13 with -Warray-bounds:

../drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c: In function 'dma_chan_tx_status':
../drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c:329:46: warning: array subscript 0 is outside array bounds of 'struct
virt_dma_desc[46116860184273879]' [-Warray-bounds=]
  329 |                 bytes = vd_to_axi_desc(vdesc)->length;
      |                                              ^~

Fixes: 8e55444da65c ("dmaengine: dw-axi-dmac: Support burst residue granularity")
Cc: Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
Cc: Vinod Koul <vkoul@...nel.org>
Cc: dmaengine@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
index 08af483331fd..4169e1d7d5ca 100644
--- a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
+++ b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
@@ -325,8 +325,6 @@ dma_chan_tx_status(struct dma_chan *dchan, dma_cookie_t cookie,
 		len = vd_to_axi_desc(vdesc)->hw_desc[0].len;
 		completed_length = completed_blocks * len;
 		bytes = length - completed_length;
-	} else {
-		bytes = vd_to_axi_desc(vdesc)->length;
 	}
 
 	spin_unlock_irqrestore(&chan->vc.lock, flags);
-- 
2.34.1