2018-03-13 16:58:44

by Pierre-Yves MORDRET

Subject: [PATCH v1 1/1] dmaengine: stm32-dmamux: fix a potential buffer overflow

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 <[email protected]>
Signed-off-by: Pierre-Yves MORDRET <[email protected]>
---
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

2018-03-22 05:18:48

by Vinod Koul

Subject: Re: [PATCH v1 1/1] dmaengine: stm32-dmamux: fix a potential buffer overflow

On Tue, Mar 13, 2018 at 05:55:35PM +0100, Pierre-Yves MORDRET wrote:
> 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.

Applied, thanks

--
~Vinod