Re: [PATCH RFC] media: videobuf2: fix the length check for mmap
From: Mauro Carvalho Chehab
Date: Mon Apr 22 2013 - 07:52:41 EST
Em 21-04-2013 19:38, Laurent Pinchart escreveu:
Hi Mauro,
On Friday 19 April 2013 08:18:01 Mauro Carvalho Chehab wrote:
Em Fri, 19 Apr 2013 15:16:56 +0530 Prabhakar lad escreveu:
From: Lad, Prabhakar <prabhakar.csengg@xxxxxxxxx>
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@xxxxxxxxx>
Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Cc: Seung-Woo Kim <sw0312.kim@xxxxxxxxxxx>
Cc: Hans Verkuil <hans.verkuil@xxxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
---
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.
I don't think we should round vb->v4l2_planes[plane].length up. That variable
stores the buffer length required by the driver, and will be used to perform
size checks when importing a dmabuf buffer. We don't want to prevent a buffer
large enough for the driver but not page size aligned to be imported.
What we could do is round in the core the size passed to the alloc function,
without storing the rounded value in vb->v4l2_planes[plane].length.
And, reading down, I realize that this is exactly what you meant :-)
Yes. Touching at .length would have side effects, but touching at
buffer's .size seem ok and VB2 dma contig code already does that
with the current code.
The proposed patch looks good to me.
Good.
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).
A comment is definitely a good idea.
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).
Agreed. The memory allocator shouldn't need to guess the core requirements.
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@xxxxxxxxx>
Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
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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