On Wed, May 03, 2017 at 01:10:26PM +0100, Robin Murphy wrote:

On 25/04/17 19:22, Catalin Marinas wrote:

quoted

The dma_common_pages_remap() function allocates a vm_struct object and
initialises the pages pointer to value passed as argument. However, when
this function is called dma_common_contiguous_remap(), the pages array
is only temporarily allocated, being freed shortly after
dma_common_contiguous_remap() returns. Architecture code checking the
validity of an area->pages pointer would incorrectly dereference already
freed pointers. This has been exposed by the arm64 commit 44176bb38fa4
("arm64: Add support for DMA_ATTR_FORCE_CONTIGUOUS to IOMMU").

Fixes: 513510ddba96 ("common: dma-mapping: introduce common remapping functions")
Cc: Laura Abbott <redacted>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reported-by: Andrzej Hajda <redacted>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
---

This is for correctness since once the arm64's mmap and get_sgtable ops
are fixed for DMA_ATTR_FORCE_CONTIGUOUS, we would no longer see the
issue. Anyway, it's better to get this fixed in case others trip over a
similar issue. I added a "Fixes" tag for completeness but I'm not sure
it's worth back-porting.

 drivers/base/dma-mapping.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/drivers/base/dma-mapping.c b/drivers/base/dma-mapping.c
index efd71cf4fdea..ab7071041141 100644
--- a/drivers/base/dma-mapping.c
+++ b/drivers/base/dma-mapping.c

@@ -277,8 +277,8 @@ EXPORT_SYMBOL(dma_common_mmap);
  * remaps an array of PAGE_SIZE pages into another vm_area
  * Cannot be used in non-sleeping contexts
  */

Nit: the above comment ends up in the wrong place now (it should still
belong to dma_common_pages_remap()).

Good point, thanks. I'll send a v2 to Greg as we don't really have a
dependency on this on arm64 (once the DMA_ATTR_FORCE_CONTIGUOUS patch is
fixed or reverted).

-- 
Catalin