ACK/Cmnt: [SRU][L/K/J][PATCH 1/1] UBUNTU: SAUCE: overlayfs: fix reference count mismatch

[Stefan Bader]

On 22.06.23 11:37, Andrea Righi wrote:
> BugLink: https://bugs.launchpad.net/bugs/2016398
> 
> Opened files reported in /proc/pid/map_files can be shows with the wrong
> mount point using overlayfs with filesystem namspaces.
> 
> This incorrect behavior is fixed:
> 
>    UBUNTU: SAUCE: overlayfs: fix incorrect mnt_id of files opened from map_files
> 
> However, the fix introduced a new regression, the reference to the
> original file stored in vma->vm_prfile is not properly released when
> vma->vm_prfile is replaced with a new file.
> 
> This can cause a reference counter unbalance, leading errors such as
> "target is busy" when trying to unmount overlayfs, even if the
> filesystem has not active reference.
> 
> Fix by properly releasing the original file stored in vm_prfile.
> 
> Fixes: 508fdae3f62dd ("UBUNTU: SAUCE: overlayfs: fix incorrect mnt_id of files opened from map_files")
> Signed-off-by: Andrea Righi <andrea.righi at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---

Kinetic may or may not be updated. It reaches EOL soon and right now 
there is no planned normal SRU cycle for it.

-Stefan

>   fs/overlayfs/file.c | 25 +++++++++++++++++++++----
>   1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index e3c6834d8d0f1..6230364ae4b41 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -504,16 +504,33 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
>    *
>    * See also mm/prfile.c
>    */
> +#ifdef CONFIG_MMU
>   static void ovl_vm_prfile_set(struct vm_area_struct *vma,
>   			      struct file *file)
>   {
>   	get_file(file);
> -	vma->vm_prfile = file;
> -#ifndef CONFIG_MMU
> +	swap(vma->vm_prfile, file);
> +	/* Drop reference count from previous file value */
> +	if (file)
> +		fput(file);
> +}
> +#else
> +static void ovl_vm_prfile_set(struct vm_area_struct *vma,
> +			      struct file *file)
> +{
> +	struct file *vm_region_file = file;
> +
>   	get_file(file);
> -	vma->vm_region->vm_prfile = file;
> -#endif
> +	get_file(vm_region_file);
> +	swap(vma->vm_prfile, file);
> +	swap(vma->vm_region->vm_prfile, vm_region_file);
> +	/* Drop reference count from previous file values */
> +	if (file)
> +		fput(file);
> +	if (vm_region_file)
> +		fput(vm_region_file);
>   }
> +#endif
>   
>   static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
>   {

-- 
- Stefan

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