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Date: Fri, 19 Apr 2013 08:18:01 -0300
From: Mauro Carvalho Chehab <mchehab@...hat.com>
To: Prabhakar lad <prabhakar.csengg@...il.com>
Cc: LMML <linux-media@...r.kernel.org>,
DLOS <davinci-linux-open-source@...ux.davincidsp.com>,
LKML <linux-kernel@...r.kernel.org>,
Hans Verkuil <hans.verkuil@...co.com>,
Pawel Osciak <pawel@...iak.com>,
Kyungmin Park <kyungmin.park@...sung.com>,
Laurent Pinchart <laurent.pinchart@...asonboard.com>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Seung-Woo Kim <sw0312.kim@...sung.com>
Subject: Re: [PATCH RFC] media: videobuf2: fix the length check for mmap
Em Fri, 19 Apr 2013 15:16:56 +0530
Prabhakar lad <prabhakar.csengg@...il.com> escreveu:
> From: Lad, Prabhakar <prabhakar.csengg@...il.com>
>
> From commit 068a0df76023926af958a336a78bef60468d2033
> "[media] media: vb2: add length check for mmap"
> patch verifies that the mmap() size requested by userspace
> doesn't exceed the buffer size.
>
> As the mmap() size is rounded up to the next page boundary
> the check will fail for buffer sizes that are not multiple
> of the page size.
>
> This patch fixes the check by aligning the buffer size to page
> size during the check. Alongside fixes the vmalloc allocator
> to round up the size.
>
> Signed-off-by: Lad, Prabhakar <prabhakar.csengg@...il.com>
> Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Seung-Woo Kim <sw0312.kim@...sung.com>
> Cc: Hans Verkuil <hans.verkuil@...co.com>
> Cc: Mauro Carvalho Chehab <mchehab@...hat.com>
> ---
> drivers/media/v4l2-core/videobuf2-core.c | 2 +-
> drivers/media/v4l2-core/videobuf2-vmalloc.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index 58c1744..223fcd4 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -1886,7 +1886,7 @@ int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma)
>
> vb = q->bufs[buffer];
>
> - if (vb->v4l2_planes[plane].length < (vma->vm_end - vma->vm_start)) {
> + if (PAGE_ALIGN(vb->v4l2_planes[plane].length) < (vma->vm_end - vma->vm_start)) {
> dprintk(1, "Invalid length\n");
> return -EINVAL;
> }
That is tricky, as it assumes that vb->v4l2_planes[plane].length was round
up to PAGE_SIZE at each memops driver, but the vb2 core doesn't enforce it.
IMO, it would be cleaner to round vb->v4l2_planes[plane].length up
at VB2 core, before calling the memops alloc functions at the drivers.
Also, VB2 is already complex enough to put it there without proper
comments (and there's a minor codingstyle issue there: line is bigger
than 80 cols).
> diff --git a/drivers/media/v4l2-core/videobuf2-vmalloc.c b/drivers/media/v4l2-core/videobuf2-vmalloc.c
> index 313d977..bf3b95c 100644
> --- a/drivers/media/v4l2-core/videobuf2-vmalloc.c
> +++ b/drivers/media/v4l2-core/videobuf2-vmalloc.c
> @@ -44,7 +44,7 @@ static void *vb2_vmalloc_alloc(void *alloc_ctx, unsigned long size, gfp_t gfp_fl
> return NULL;
>
> buf->size = size;
> - buf->vaddr = vmalloc_user(buf->size);
> + buf->vaddr = vmalloc_user(PAGE_ALIGN(buf->size));
See? You needed to put an alignment here as well, not because vmalloc
needs it, but because this is needed by VB2 core.
Also, on the other drivers, buf->size is stored page aligned, while
here, you're doing different, without any documented reason for doing
that, instead of doing the same as on the other memops drivers.
That mistake reflects, for example, when the driver prints the failure:
if (!buf->vaddr) {
pr_debug("vmalloc of size %ld failed\n", buf->size);
as it will show a different size than what you actually required.
As those memory starving errors can also produce a dump at the mm
core, the size there won't match the size on the above printed message.
Also, it is a very bad idea to delegate the core's requirement of
do page alignment from the core to the memops drivers, as other
patches may change the logic there, or a new memops could be added,
and the same problem will hit again (and unnoticed, as the check
routine do page alignments).
> buf->handler.refcount = &buf->refcount;
> buf->handler.put = vb2_vmalloc_put;
> buf->handler.arg = buf;
IMO, a cleaner version would be the following (untested) code.
-
[media] videobuf2: fix the length check for mmap
Memory maps typically require that the buffer size to be page
aligned. Currently, two memops drivers do such alignment
internally, but videobuf-vmalloc doesn't.
Also, the buffer overflow check doesn't take it into account.
So, instead of doing it at each memops driver, enforce it at
VB2 core.
Reported-by: Prabhakar lad <prabhakar.csengg@...il.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@...hat.com>
diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index 58c1744..7d833ee 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -54,10 +54,15 @@ static int __vb2_buf_mem_alloc(struct vb2_buffer *vb)
void *mem_priv;
int plane;
- /* Allocate memory for all planes in this buffer */
+ /*
+ * Allocate memory for all planes in this buffer
+ * NOTE: mmapped areas should be page aligned
+ */
for (plane = 0; plane < vb->num_planes; ++plane) {
+ unsigned long size = PAGE_ALIGN(q->plane_sizes[plane]);
+
mem_priv = call_memop(q, alloc, q->alloc_ctx[plane],
- q->plane_sizes[plane], q->gfp_flags);
+ size, q->gfp_flags);
if (IS_ERR_OR_NULL(mem_priv))
goto free;
@@ -1852,6 +1857,7 @@ int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma)
struct vb2_buffer *vb;
unsigned int buffer, plane;
int ret;
+ unsigned long length;
if (q->memory != V4L2_MEMORY_MMAP) {
dprintk(1, "Queue is not currently set up for mmap\n");
@@ -1886,8 +1892,15 @@ int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma)
vb = q->bufs[buffer];
- if (vb->v4l2_planes[plane].length < (vma->vm_end - vma->vm_start)) {
- dprintk(1, "Invalid length\n");
+ /*
+ * MMAP requires page_aligned buffers.
+ * The buffer length was page_aligned at __vb2_buf_mem_alloc(),
+ * so, we need to do the same here.
+ */
+ length = PAGE_ALIGN(vb->v4l2_planes[plane].length);
+ if (length < (vma->vm_end - vma->vm_start)) {
+ dprintk(1,
+ "MMAP invalid, as it would overflow buffer length\n");
return -EINVAL;
}
diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c
index ae35d25..fd56f25 100644
--- a/drivers/media/v4l2-core/videobuf2-dma-contig.c
+++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c
@@ -162,9 +162,6 @@ static void *vb2_dc_alloc(void *alloc_ctx, unsigned long size, gfp_t gfp_flags)
if (!buf)
return ERR_PTR(-ENOMEM);
- /* align image size to PAGE_SIZE */
- size = PAGE_ALIGN(size);
-
buf->vaddr = dma_alloc_coherent(dev, size, &buf->dma_addr,
GFP_KERNEL | gfp_flags);
if (!buf->vaddr) {
diff --git a/drivers/media/v4l2-core/videobuf2-dma-sg.c b/drivers/media/v4l2-core/videobuf2-dma-sg.c
index 59522b2..16ae3dc 100644
--- a/drivers/media/v4l2-core/videobuf2-dma-sg.c
+++ b/drivers/media/v4l2-core/videobuf2-dma-sg.c
@@ -55,7 +55,8 @@ static void *vb2_dma_sg_alloc(void *alloc_ctx, unsigned long size, gfp_t gfp_fla
buf->write = 0;
buf->offset = 0;
buf->sg_desc.size = size;
- buf->sg_desc.num_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ /* size is already page aligned */
+ buf->sg_desc.num_pages = size >> PAGE_SHIFT;
buf->sg_desc.sglist = vzalloc(buf->sg_desc.num_pages *
sizeof(*buf->sg_desc.sglist));
--
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