Re: [PATCH 1/6] mm: mmap: fix fput in error path

Re: [PATCH 1/6] mm: mmap: fix fput in error path

[linmiaohe]

Jason Gunthorpe <jgg@ziepe.ca> wrote:
> On Fri, Oct 09, 2020 at 03:04:20PM -0700, Andrew Morton wrote:
>> On Fri,  9 Oct 2020 17:03:37 +0200 "Christian König" <ckoenig.leichtzumerken@gmail.com> wrote:
>> 
>> > Patch "495c10cc1c0c CHROMIUM: dma-buf: restore args..."
>> > adds a workaround for a bug in mmap_region.
>> > 
>> > As the comment states ->mmap() callback can change
>> > vma->vm_file and so we might call fput() on the wrong file.
>> > 
>> > Revert the workaround and proper fix this in mmap_region.
>> > 
>> 
>> Doesn't this patch series address the same thing as 
>> https://lkml.kernel.org/r/20200916090733.31427-1-linmiaohe@huawei.com?
>
>Same basic issue, looks like both of these patches should be combined to plug it fully.
>
>Jason 

I think so too. Both of these patches fix the fput at possible wrong @file due to ->mmap() callback can change vma->vm_file.

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Re: [PATCH 1/6] mm: mmap: fix fput in error path

[Christian König]

Am 10.10.20 um 00:25 schrieb Jason Gunthorpe:
> On Fri, Oct 09, 2020 at 03:04:20PM -0700, Andrew Morton wrote:
>> On Fri,  9 Oct 2020 17:03:37 +0200 "Christian König" <ckoenig.leichtzumerken@gmail.com> wrote:
>>
>>> Patch "495c10cc1c0c CHROMIUM: dma-buf: restore args..."
>>> adds a workaround for a bug in mmap_region.
>>>
>>> As the comment states ->mmap() callback can change
>>> vma->vm_file and so we might call fput() on the wrong file.
>>>
>>> Revert the workaround and proper fix this in mmap_region.
>>>
>> Doesn't this patch series address the same thing as
>> https://lkml.kernel.org/r/20200916090733.31427-1-linmiaohe@huawei.com?
> Same basic issue, looks like both of these patches should be combined
> to plug it fully.

Yes, agree completely.

It's a different error path, but we need to fix both occasions.

Christian.

>
> Jason

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Re: [PATCH 1/6] mm: mmap: fix fput in error path

[Jason Gunthorpe]

On Fri, Oct 09, 2020 at 03:04:20PM -0700, Andrew Morton wrote:
> On Fri,  9 Oct 2020 17:03:37 +0200 "Christian König" <ckoenig.leichtzumerken@gmail.com> wrote:
> 
> > Patch "495c10cc1c0c CHROMIUM: dma-buf: restore args..."
> > adds a workaround for a bug in mmap_region.
> > 
> > As the comment states ->mmap() callback can change
> > vma->vm_file and so we might call fput() on the wrong file.
> > 
> > Revert the workaround and proper fix this in mmap_region.
> > 
> 
> Doesn't this patch series address the same thing as
> https://lkml.kernel.org/r/20200916090733.31427-1-linmiaohe@huawei.com?

Same basic issue, looks like both of these patches should be combined
to plug it fully.

Jason 
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Re: [PATCH 1/6] mm: mmap: fix fput in error path

[Andrew Morton]

On Fri,  9 Oct 2020 17:03:37 +0200 "Christian König" <ckoenig.leichtzumerken@gmail.com> wrote:

> Patch "495c10cc1c0c CHROMIUM: dma-buf: restore args..."
> adds a workaround for a bug in mmap_region.
> 
> As the comment states ->mmap() callback can change
> vma->vm_file and so we might call fput() on the wrong file.
> 
> Revert the workaround and proper fix this in mmap_region.
> 

Doesn't this patch series address the same thing as
https://lkml.kernel.org/r/20200916090733.31427-1-linmiaohe@huawei.com?

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Re: [PATCH 1/6] mm: mmap: fix fput in error path

[Jason Gunthorpe]

On Fri, Oct 09, 2020 at 05:03:37PM +0200, Christian König wrote:
> Patch "495c10cc1c0c CHROMIUM: dma-buf: restore args..."
> adds a workaround for a bug in mmap_region.
> 
> As the comment states ->mmap() callback can change
> vma->vm_file and so we might call fput() on the wrong file.
> 
> Revert the workaround and proper fix this in mmap_region.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
>  drivers/dma-buf/dma-buf.c | 22 +++++-----------------
>  mm/mmap.c                 |  2 +-
>  2 files changed, 6 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index a6ba4d598f0e..edd57402a48a 100644
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -1143,9 +1143,6 @@ EXPORT_SYMBOL_GPL(dma_buf_end_cpu_access);
>  int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
>  		 unsigned long pgoff)
>  {
> -	struct file *oldfile;
> -	int ret;
> -
>  	if (WARN_ON(!dmabuf || !vma))
>  		return -EINVAL;
>  
> @@ -1163,22 +1160,13 @@ int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
>  		return -EINVAL;
>  
>  	/* readjust the vma */
> -	get_file(dmabuf->file);
> -	oldfile = vma->vm_file;
> -	vma->vm_file = dmabuf->file;
> -	vma->vm_pgoff = pgoff;
> +	if (vma->vm_file)
> +		fput(vma->vm_file);

This if is redundant too

But otherwise

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Thanks,
Jason
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[PATCH 1/6] mm: mmap: fix fput in error path

[Christian König]

Patch "495c10cc1c0c CHROMIUM: dma-buf: restore args..."
adds a workaround for a bug in mmap_region.

As the comment states ->mmap() callback can change
vma->vm_file and so we might call fput() on the wrong file.

Revert the workaround and proper fix this in mmap_region.

Signed-off-by: Christian König <christian.koenig@amd.com>
---
 drivers/dma-buf/dma-buf.c | 22 +++++-----------------
 mm/mmap.c                 |  2 +-
 2 files changed, 6 insertions(+), 18 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index a6ba4d598f0e..edd57402a48a 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -1143,9 +1143,6 @@ EXPORT_SYMBOL_GPL(dma_buf_end_cpu_access);
 int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
 		 unsigned long pgoff)
 {
-	struct file *oldfile;
-	int ret;
-
 	if (WARN_ON(!dmabuf || !vma))
 		return -EINVAL;
 
@@ -1163,22 +1160,13 @@ int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
 		return -EINVAL;
 
 	/* readjust the vma */
-	get_file(dmabuf->file);
-	oldfile = vma->vm_file;
-	vma->vm_file = dmabuf->file;
-	vma->vm_pgoff = pgoff;
+	if (vma->vm_file)
+		fput(vma->vm_file);
 
-	ret = dmabuf->ops->mmap(dmabuf, vma);
-	if (ret) {
-		/* restore old parameters on failure */
-		vma->vm_file = oldfile;
-		fput(dmabuf->file);
-	} else {
-		if (oldfile)
-			fput(oldfile);
-	}
-	return ret;
+	vma->vm_file = get_file(dmabuf->file);
+	vma->vm_pgoff = pgoff;
 
+	return dmabuf->ops->mmap(dmabuf, vma);
 }
 EXPORT_SYMBOL_GPL(dma_buf_mmap);
 
diff --git a/mm/mmap.c b/mm/mmap.c
index 40248d84ad5f..3a2670d73355 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1852,8 +1852,8 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	return addr;
 
 unmap_and_free_vma:
+	fput(vma->vm_file);
 	vma->vm_file = NULL;
-	fput(file);
 
 	/* Undo any partial mapping done by a device driver. */
 	unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);
-- 
2.17.1

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