2020-06-15 01:12:34

by Jianqun Xu

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

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 <[email protected]>
---
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

2020-06-15 08:37:16

by David Hildenbrand

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

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 <[email protected]>
> ---
> 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 <[email protected]>


--
Thanks,

David / dhildenb