Re: [PATCH] perf/core: Fix refcount bug and potential UAF in perf_mmap

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Feb 01, 2026 at 07:34:36PM +0800, Haocheng Yu wrote:
> The issue is caused by a race condition between mmap() and event
> teardown. In perf_mmap(), the ring_buffer (rb) is accessed via
> map_range() after the mmap_mutex is released. If another thread
> closes the event or detaches the buffer during this window, the
> reference count of rb can drop to zero, leading to a UAF or
> refcount saturation when map_range() or subsequent logic attempts
> to use it.
> 
> Fix this by extending the scope of mmap_mutex to cover the entire
> setup process, including map_range(), ensuring the buffer remains
> valid until the mapping is complete.
> 
> Signed-off-by: Haocheng Yu <yuhaocheng035@gmail.com>
> ---
>  kernel/events/core.c | 42 +++++++++++++++++++++---------------------
>  1 file changed, 21 insertions(+), 21 deletions(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 2c35acc2722b..7c93f7d057cb 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7167,28 +7167,28 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
>  			ret = perf_mmap_aux(vma, event, nr_pages);
>  		if (ret)
>  			return ret;
> -	}
> -
> -	/*
> -	 * Since pinned accounting is per vm we cannot allow fork() to copy our
> -	 * vma.
> -	 */
> -	vm_flags_set(vma, VM_DONTCOPY | VM_DONTEXPAND | VM_DONTDUMP);
> -	vma->vm_ops = &perf_mmap_vmops;
>  
> -	mapped = get_mapped(event, event_mapped);
> -	if (mapped)
> -		mapped(event, vma->vm_mm);
> -
> -	/*
> -	 * Try to map it into the page table. On fail, invoke
> -	 * perf_mmap_close() to undo the above, as the callsite expects
> -	 * full cleanup in this case and therefore does not invoke
> -	 * vmops::close().
> -	 */
> -	ret = map_range(event->rb, vma);
> -	if (ret)
> -		perf_mmap_close(vma);
> +	/*
> +	 * Since pinned accounting is per vm we cannot allow fork() to copy our
> +	 * vma.
> +	 */
> +	vm_flags_set(vma, VM_DONTCOPY | VM_DONTEXPAND | VM_DONTDUMP);
> +	vma->vm_ops = &perf_mmap_vmops;
> +
> +	mapped = get_mapped(event, event_mapped);
> +	if (mapped)
> +		mapped(event, vma->vm_mm);
> +
> +	/*
> +	 * Try to map it into the page table. On fail, invoke
> +	 * perf_mmap_close() to undo the above, as the callsite expects
> +	 * full cleanup in this case and therefore does not invoke
> +	 * vmops::close().
> +	 */
> +	ret = map_range(event->rb, vma);
> +	if (ret)
> +		perf_mmap_close(vma);
> +	}


This indentation looks very odd, are you sure it is correct?

thanks,

greg k-h