[PATCH] drm/buddy: fixup potential uaf

[PATCH] drm/buddy: fixup potential uaf

[Matthew Auld]

If we are unlucky and somehow can't allocate enough memory when
splitting blocks, where we temporarily end up with the given block and
its buddy on the respective free list, then we need to ensure we delete
both blocks, and not just the buddy, before potentially freeing them.

v2: rebase on i915_buddy removal

Fixes: 14d1b9a6247c ("drm/i915: buddy allocator")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Arunpravin <Arunpravin.PaneerSelvam@amd.com>
Cc: Christian König <christian.koenig@amd.com>
---
 drivers/gpu/drm/drm_buddy.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
index d60878bc9c20..2bf75e8abfaa 100644
--- a/drivers/gpu/drm/drm_buddy.c
+++ b/drivers/gpu/drm/drm_buddy.c
@@ -333,8 +333,10 @@ drm_buddy_alloc_blocks(struct drm_buddy *mm, unsigned int order)
 	return block;
 
 out_free:
-	if (i != order)
+	if (i != order) {
+		list_del(&block->link);
 		__drm_buddy_free(mm, block);
+	}
 	return ERR_PTR(err);
 }
 EXPORT_SYMBOL(drm_buddy_alloc_blocks);
@@ -452,8 +454,10 @@ int drm_buddy_alloc_range(struct drm_buddy *mm,
 	buddy = get_buddy(block);
 	if (buddy &&
 	    (drm_buddy_block_is_free(block) &&
-	     drm_buddy_block_is_free(buddy)))
+	     drm_buddy_block_is_free(buddy))) {
+		list_del(&block->link);
 		__drm_buddy_free(mm, block);
+	}
 
 err_free:
 	drm_buddy_free_list(mm, &allocated);
-- 
2.34.1

Re: [PATCH] drm/buddy: fixup potential uaf

[Daniel Vetter]

On Tue, Feb 08, 2022 at 11:38:15AM +0000, Matthew Auld wrote:
> If we are unlucky and somehow can't allocate enough memory when
> splitting blocks, where we temporarily end up with the given block and
> its buddy on the respective free list, then we need to ensure we delete
> both blocks, and not just the buddy, before potentially freeing them.
> 
> v2: rebase on i915_buddy removal
> 
> Fixes: 14d1b9a6247c ("drm/i915: buddy allocator")
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Arunpravin <Arunpravin.PaneerSelvam@amd.com>
> Cc: Christian König <christian.koenig@amd.com>

btw wrt fixups, can you pls include the drm_buddy.c kerneldoc into
Documentation/gpu/drm-mm.rst? That seems to be missing. Also probably some
kerneldoc to polish to make it warning free and complete.
-Daniel

> ---
>  drivers/gpu/drm/drm_buddy.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
> index d60878bc9c20..2bf75e8abfaa 100644
> --- a/drivers/gpu/drm/drm_buddy.c
> +++ b/drivers/gpu/drm/drm_buddy.c
> @@ -333,8 +333,10 @@ drm_buddy_alloc_blocks(struct drm_buddy *mm, unsigned int order)
>  	return block;
>  
>  out_free:
> -	if (i != order)
> +	if (i != order) {
> +		list_del(&block->link);
>  		__drm_buddy_free(mm, block);
> +	}
>  	return ERR_PTR(err);
>  }
>  EXPORT_SYMBOL(drm_buddy_alloc_blocks);
> @@ -452,8 +454,10 @@ int drm_buddy_alloc_range(struct drm_buddy *mm,
>  	buddy = get_buddy(block);
>  	if (buddy &&
>  	    (drm_buddy_block_is_free(block) &&
> -	     drm_buddy_block_is_free(buddy)))
> +	     drm_buddy_block_is_free(buddy))) {
> +		list_del(&block->link);
>  		__drm_buddy_free(mm, block);
> +	}
>  
>  err_free:
>  	drm_buddy_free_list(mm, &allocated);
> -- 
> 2.34.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch