[PATCH] mm/cma: fix NULL pointer dereference when cma could not be activated

[PATCH] mm/cma: fix NULL pointer dereference when cma could not be activated

[Jianqun Xu]

In some case the cma area could not be activated, but the cma_alloc be
used under this case, then the kernel will crash caused by NULL pointer
dereference.

Add bitmap valid check in cma_alloc to avoid this issue.

Signed-off-by: Jianqun Xu <jay.xu@rock-chips.com>
---
 mm/cma.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/cma.c b/mm/cma.c
index 0463ad2ce06b..488496fa2972 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -425,7 +425,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
 	struct page *page = NULL;
 	int ret = -ENOMEM;
 
-	if (!cma || !cma->count)
+	if (!cma || !cma->count || !cma->bitmap)
 		return NULL;
 
 	pr_debug("%s(cma %p, count %zu, align %d)\n", __func__, (void *)cma,
-- 
2.17.1

Re: [PATCH] mm/cma: fix NULL pointer dereference when cma could not be activated

[David Hildenbrand]

On 15.06.20 03:01, Jianqun Xu wrote:
> In some case the cma area could not be activated, but the cma_alloc be
> used under this case, then the kernel will crash caused by NULL pointer
> dereference.
> 
> Add bitmap valid check in cma_alloc to avoid this issue.
> 
> Signed-off-by: Jianqun Xu <jay.xu@rock-chips.com>
> ---
>  mm/cma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/cma.c b/mm/cma.c
> index 0463ad2ce06b..488496fa2972 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -425,7 +425,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
>  	struct page *page = NULL;
>  	int ret = -ENOMEM;
>  
> -	if (!cma || !cma->count)
> +	if (!cma || !cma->count || !cma->bitmap)
>  		return NULL;
>  
>  	pr_debug("%s(cma %p, count %zu, align %d)\n", __func__, (void *)cma,
> 

If cma_activate_area() fails, cma_init_reserved_areas() fails. AFAIKS,
init/main.c will ignore any errors via do_one_initcall(). So this seems
to be possible.

Reviewed-by: David Hildenbrand <david@redhat.com>


-- 
Thanks,

David / dhildenb