diff mbox series

[1/2] mm: mmap: fix fput in error path v2

Message ID 20201106114806.46015-2-christian.koenig@amd.com (mailing list archive)
State New, archived
Headers show
Series [1/2] mm: mmap: fix fput in error path v2 | expand

Commit Message

Christian König Nov. 6, 2020, 11:48 a.m. UTC 
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.

v2: drop the extra if in dma_buf_mmap as well

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
---
 drivers/dma-buf/dma-buf.c | 20 +++-----------------
 mm/mmap.c                 |  2 +-
 2 files changed, 4 insertions(+), 18 deletions(-)

Comments

Andrew Morton Nov. 6, 2020, 10:48 p.m. UTC | #1 
On Fri,  6 Nov 2020 12:48:05 +0100 "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.
> 

Seems correct, best I can tell.  Presumably all ->mmap() instances will
correctly fput() to original file* if they're rewriting vma->vm_file.
Christian König Nov. 18, 2020, 10:57 a.m. UTC | #2 
Am 06.11.20 um 23:48 schrieb Andrew Morton:
> On Fri,  6 Nov 2020 12:48:05 +0100 "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.
>>
> Seems correct, best I can tell.  Presumably all ->mmap() instances will
> correctly fput() to original file* if they're rewriting vma->vm_file.

Yes, exactly.

Patch #2 provides a helper to make sure that everybody gets the 
get_file()/fput() correctly while updating vma->vm_file.

Can I add your acked-by to the patches and push them upstream through 
drm-misc-next?

Thanks,
Christian.
Andrew Morton Nov. 18, 2020, 10:27 p.m. UTC | #3 
On Wed, 18 Nov 2020 11:57:44 +0100 Christian König <ckoenig.leichtzumerken@gmail.com> wrote:

> Am 06.11.20 um 23:48 schrieb Andrew Morton:
> > On Fri,  6 Nov 2020 12:48:05 +0100 "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.
> >>
> > Seems correct, best I can tell.  Presumably all ->mmap() instances will
> > correctly fput() to original file* if they're rewriting vma->vm_file.
> 
> Yes, exactly.
> 
> Patch #2 provides a helper to make sure that everybody gets the 
> get_file()/fput() correctly while updating vma->vm_file.
> 
> Can I add your acked-by to the patches and push them upstream through 
> drm-misc-next?

Please go ahead.

Acked-by: Andrew Morton <akpm@linux-foundation.org>
diff mbox series

Patch

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 0eb80c1ecdab..282bd8b84170 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -1166,9 +1166,6 @@  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;
 
@@ -1186,22 +1183,11 @@  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;
+	fput(vma->vm_file);
+	vma->vm_file = get_file(dmabuf->file);
 	vma->vm_pgoff = pgoff;
 
-	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;
-
+	return dmabuf->ops->mmap(dmabuf, vma);
 }
 EXPORT_SYMBOL_GPL(dma_buf_mmap);
 
diff --git a/mm/mmap.c b/mm/mmap.c
index d91ecb00d38c..30a4e8412a58 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1899,8 +1899,8 @@  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);