linux-kernel - [PATCH] dmaengine: Fix access to uninitialized dma_slave

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Message-Id: <ca92998ccc054b4f2bfd60ef3adbab2913171eac.1575546234.git.lukas@wunner.de>
Date:   Thu, 5 Dec 2019 12:54:49 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     dmaengine@...r.kernel.org, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH] dmaengine: Fix access to uninitialized dma_slave_caps

dmaengine_desc_set_reuse() allocates a struct dma_slave_caps on the
stack, populates it using dma_get_slave_caps() and then accesses one
of its members.

However dma_get_slave_caps() may fail and this isn't accounted for,
leading to a legitimate warning of gcc-4.9 (but not newer versions):

   In file included from drivers/spi/spi-bcm2835.c:19:0:
   drivers/spi/spi-bcm2835.c: In function 'dmaengine_desc_set_reuse':
>> include/linux/dmaengine.h:1370:10: warning: 'caps.descriptor_reuse' is used uninitialized in this function [-Wuninitialized]
     if (caps.descriptor_reuse) {

Fix it, thereby also silencing the gcc-4.9 warning.

The issue has been present for 4 years but surfaces only now that
the first caller of dmaengine_desc_set_reuse() has been added in
spi-bcm2835.c. Another user of reusable DMA descriptors has existed
for a while in pxa_camera.c, but it sets the DMA_CTRL_REUSE flag
directly instead of calling dmaengine_desc_set_reuse(). Nevertheless,
tag this commit for stable in case there are out-of-tree users.

Fixes: 272420214d26 ("dmaengine: Add DMA_CTRL_REUSE")
Reported-by: kbuild test robot <lkp@...el.com>
Signed-off-by: Lukas Wunner <lukas@...ner.de>
Cc: stable@...r.kernel.org # v4.3+
---
 include/linux/dmaengine.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 8fcdee1c0cf9..dad4a68fa009 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -1364,8 +1364,11 @@ static inline int dma_get_slave_caps(struct dma_chan *chan,
 static inline int dmaengine_desc_set_reuse(struct dma_async_tx_descriptor *tx)
 {
 	struct dma_slave_caps caps;
+	int ret;

-	dma_get_slave_caps(tx->chan, &caps);
+	ret = dma_get_slave_caps(tx->chan, &caps);
+	if (ret)
+		return ret;

 	if (caps.descriptor_reuse) {
 		tx->flags |= DMA_CTRL_REUSE;
-- 
2.24.0