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Date: Wed, 24 Dec 2008 10:36:23 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
linux-kernel@...r.kernel.org,
Dmitry Baryshkov <dbaryshkov@...il.com>
Subject: Re: [mmotm 2008-12-22-16-14] NULL pointer dereference in
dma_alloc_from_coherent().
On Wed, 24 Dec 2008 16:45:02 +0100 Johannes Weiner <hannes@...xchg.org> wrote:
> >
> > This thing was rather stupidly coded. Rework it all prior to making
> > changes.
> >
> > Also, rename local variable `page': kernel readers expect something called
> > `page' to have type `struct page *'.
> >
> > Cc: Guennadi Liakhovetski <lg@...x.de>
> > Cc: Johannes Weiner <hannes@...xchg.org>
> > Cc: Pekka Enberg <penberg@...helsinki.fi>
> > Cc: Dmitry Baryshkov <dbaryshkov@...il.com>
> > Cc: Jesse Barnes <jbarnes@...tuousgeek.org>
> > Cc: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> > ---
> >
> > kernel/dma-coherent.c | 27 ++++++++++++++++-----------
> > 1 file changed, 16 insertions(+), 11 deletions(-)
> >
> > diff -puN kernel/dma-coherent.c~dma_alloc_coherent-clean-it-up kernel/dma-coherent.c
> > --- a/kernel/dma-coherent.c~dma_alloc_coherent-clean-it-up
> > +++ a/kernel/dma-coherent.c
> > @@ -109,20 +109,25 @@ EXPORT_SYMBOL(dma_mark_declared_memory_o
> > int dma_alloc_from_coherent(struct device *dev, ssize_t size,
> > dma_addr_t *dma_handle, void **ret)
> > {
> > - struct dma_coherent_mem *mem = dev ? dev->dma_mem : NULL;
> > + struct dma_coherent_mem *mem;
> > int order = get_order(size);
> > + int pageno;
> > +
> > + if (!dev)
> > + return 0;
> > + mem = dev->dma_mem;
> > + if (!mem)
> > + return 0;
> >
> > - if (mem) {
> > - int page = bitmap_find_free_region(mem->bitmap, mem->size,
> > - order);
> > - if (page >= 0) {
> > - *dma_handle = mem->device_base + (page << PAGE_SHIFT);
> > - *ret = mem->virt_base + (page << PAGE_SHIFT);
> > - memset(*ret, 0, size);
> > - } else if (mem->flags & DMA_MEMORY_EXCLUSIVE)
> > - *ret = NULL;
> > + pageno = bitmap_find_free_region(mem->bitmap, mem->size, order);
> > + if (pageno >= 0) {
> > + *dma_handle = mem->device_base + (pageno << PAGE_SHIFT);
> > + *ret = mem->virt_base + (pageno << PAGE_SHIFT);
> > + memset(*ret, 0, size);
> > + } else if (mem->flags & DMA_MEMORY_EXCLUSIVE) {
> > + *ret = NULL;
> > }
> > - return (mem != NULL);
> > + return 1;
> > }
> > EXPORT_SYMBOL(dma_alloc_from_coherent);
>
> Yep, looks much better.
>
Looking at it again, that function has a bug:
int dma_alloc_from_coherent(struct device *dev, ssize_t size,
dma_addr_t *dma_handle, void **ret)
{
struct dma_coherent_mem *mem = dev ? dev->dma_mem : NULL;
int order = get_order(size);
if (mem) {
int page = bitmap_find_free_region(mem->bitmap, mem->size,
order);
if (page >= 0) {
*dma_handle = mem->device_base + (page << PAGE_SHIFT);
*ret = mem->virt_base + (page << PAGE_SHIFT);
memset(*ret, 0, size);
} else if (mem->flags & DMA_MEMORY_EXCLUSIVE)
*ret = NULL;
}
return (mem != NULL);
}
if bitmap_find_free_region() fails and DMA_MEMORY_EXCLUSIVE is not set,
the function will fail to write anything to *ret and will return 1.
This will cause dma_alloc_coherent() to return an uninitialised value,
crashing the kernel, perhaps via DMA to a random address (ugh).
So I think it should do this:
int dma_alloc_from_coherent(struct device *dev, ssize_t size,
dma_addr_t *dma_handle, void **ret)
{
struct dma_coherent_mem *mem = dev ? dev->dma_mem : NULL;
int order = get_order(size);
if (mem) {
int page = bitmap_find_free_region(mem->bitmap, mem->size,
order);
if (page >= 0) {
/*
* Memory was found in the per-device arena.
*/
*dma_handle = mem->device_base + (page << PAGE_SHIFT);
*ret = mem->virt_base + (page << PAGE_SHIFT);
memset(*ret, 0, size);
} else if (mem->flags & DMA_MEMORY_EXCLUSIVE) {
/*
* The per-device arena is exhausted and we are not
* permitted to fall back to generic memory.
*/
*ret = NULL;
} else {
/*
* The per-device arena is exhausted and we are
* permitted to fall back to generic memory.
*/
return 0;
}
}
return (mem != NULL);
}
Can I have some review of this, please?
From: Andrew Morton <akpm@...ux-foundation.org>
If bitmap_find_free_region() fails and DMA_MEMORY_EXCLUSIVE is not set,
the function will fail to write anything to *ret and will return 1. This will cause dma_alloc_coherent() to return an uninitialised value,
crashing the kernel, perhaps via DMA to a random address.
Fix that by changing it to return zero in this case, so the caller will
proceed to allocate the memory from the generic memory allocator.
Cc: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc: Dmitry Baryshkov <dbaryshkov@...il.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Johannes Weiner <hannes@...xchg.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
kernel/dma-coherent.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff -puN kernel/dma-coherent.c~dma_alloc_from_coherent-fix-fallback-to-generic-memory kernel/dma-coherent.c
--- a/kernel/dma-coherent.c~dma_alloc_from_coherent-fix-fallback-to-generic-memory
+++ a/kernel/dma-coherent.c
@@ -116,11 +116,25 @@ int dma_alloc_from_coherent(struct devic
int page = bitmap_find_free_region(mem->bitmap, mem->size,
order);
if (page >= 0) {
+ /*
+ * Memory was found in the per-device arena.
+ */
*dma_handle = mem->device_base + (page << PAGE_SHIFT);
*ret = mem->virt_base + (page << PAGE_SHIFT);
memset(*ret, 0, size);
- } else if (mem->flags & DMA_MEMORY_EXCLUSIVE)
+ } else if (mem->flags & DMA_MEMORY_EXCLUSIVE) {
+ /*
+ * The per-device arena is exhausted and we are not
+ * permitted to fall back to generic memory.
+ */
*ret = NULL;
+ } else {
+ /*
+ * The per-device arena is exhausted and we are
+ * permitted to fall back to generic memory.
+ */
+ return 0;
+ }
}
return (mem != NULL);
}
_
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