From mboxrd@z Thu Jan 1 00:00:00 1970 From: pierre-yves.mordret@st.com (Pierre-Yves MORDRET) Date: Tue, 13 Mar 2018 17:55:35 +0100 Subject: [PATCH v1 1/1] dmaengine: stm32-dmamux: fix a potential buffer overflow Message-ID: <1520960135-26575-1-git-send-email-pierre-yves.mordret@st.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org The bitfield dma_inuse is allocated of size dma_requests bits, thus a valid bit address is from 0 to (dma_requests - 1). When find_first_zero_bit() fails, it returns dma_requests as invalid address. Using such address for the following set_bit() is incorrect and, if dma_requests is a multiple of BITS_PER_LONG, it will cause a buffer overflow. Currently this driver is only used in DT stm32h743.dtsi where a safe value dma_requests=16 is not triggering the buffer overflow. Fixed by checking the return value of find_first_zero_bit() _before_ using it. Signed-off-by: Antonio Borneo Signed-off-by: Pierre-Yves MORDRET --- Version history: v1: * Initial --- --- drivers/dma/stm32-dmamux.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/drivers/dma/stm32-dmamux.c b/drivers/dma/stm32-dmamux.c index 4dbb30c..b922db9 100644 --- a/drivers/dma/stm32-dmamux.c +++ b/drivers/dma/stm32-dmamux.c @@ -118,14 +118,15 @@ static void *stm32_dmamux_route_allocate(struct of_phandle_args *dma_spec, spin_lock_irqsave(&dmamux->lock, flags); mux->chan_id = find_first_zero_bit(dmamux->dma_inuse, dmamux->dma_requests); - set_bit(mux->chan_id, dmamux->dma_inuse); - spin_unlock_irqrestore(&dmamux->lock, flags); if (mux->chan_id == dmamux->dma_requests) { + spin_unlock_irqrestore(&dmamux->lock, flags); dev_err(&pdev->dev, "Run out of free DMA requests\n"); ret = -ENOMEM; - goto error; + goto error_chan_id; } + set_bit(mux->chan_id, dmamux->dma_inuse); + spin_unlock_irqrestore(&dmamux->lock, flags); /* Look for DMA Master */ for (i = 1, min = 0, max = dmamux->dma_reqs[i]; @@ -173,6 +174,8 @@ static void *stm32_dmamux_route_allocate(struct of_phandle_args *dma_spec, error: clear_bit(mux->chan_id, dmamux->dma_inuse); + +error_chan_id: kfree(mux); return ERR_PTR(ret); } -- 2.7.4