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SubjectRe: [PATCH 1/2] mm: mmap: fix fput in error path v2
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If nobody comes up with an objections I'm going to merge that through 
drm-misc-next.

Thanks,
Christian.

Am 12.10.20 um 10:52 schrieb 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.
>
> 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(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index a6ba4d598f0e..08630d057cf2 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 +1160,11 @@ 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 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);

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