Re: [mmotm 2008-12-22-16-14] NULL pointer dereference in dma_alloc_from_coherent().

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 24 Dec 2008 15:34:06 +0900 Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> wrote:

> IP: [<c0159475>] dma_alloc_from_coherent+0x35/0xa0

Thanks.

dma-coherent-catch-oversized-requests-to-dma_alloc_from_coherent.patch does

--- a/kernel/dma-coherent.c~dma-coherent-catch-oversized-requests-to-dma_alloc_from_coherent
+++ a/kernel/dma-coherent.c
@@ -112,6 +112,9 @@ int dma_alloc_from_coherent(struct devic
 	struct dma_coherent_mem *mem = dev ? dev->dma_mem : NULL;
 	int order = get_order(size);
 
+	if (unlikely(size > mem->size))
+		return 0;
+
 	if (mem) {
 		int page = bitmap_find_free_region(mem->bitmap, mem->size,
 						     order);

which can plainly oops if dev==NULL or if dev->dma_mem=NULL.

That function is fairly stinky, so prior to altering it, let's clean it up:

From: Andrew Morton <akpm@linux-foundation.org>

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@denx.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Dmitry Baryshkov <dbaryshkov@gmail.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-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);
 
_



Then
dma-coherent-catch-oversized-requests-to-dma_alloc_from_coherent.patch
becomes:

--- a/kernel/dma-coherent.c~dma-coherent-catch-oversized-requests-to-dma_alloc_from_coherent
+++ a/kernel/dma-coherent.c
@@ -118,6 +118,8 @@ int dma_alloc_from_coherent(struct devic
 	mem = dev->dma_mem;
 	if (!mem)
 		return 0;
+	if (unlikely(size > mem->size))
+ 		return 0;
 
 	pageno = bitmap_find_free_region(mem->bitmap, mem->size, order);
 	if (pageno >= 0) {
_