2021-03-16 15:18:13

by Colin King

Subject: [PATCH] mm: cma: Fix potential null dereference on pointer cma

From: Colin Ian King <[email protected]>

At the start of the function there is a null pointer check on cma
and then branch to error handling label 'out'. The subsequent call
to cma_sysfs_fail_pages_count dereferences cma, hence there is a
potential null pointer deference issue. Fix this by only calling
cma_sysfs_fail_pages_count if cma is not null.

Addresses-Coverity: ("Dereference after null check")
Fixes: dc4764f7e9ac ("mm: cma: support sysfs")
Signed-off-by: Colin Ian King <[email protected]>
---
mm/cma.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/cma.c b/mm/cma.c
index 6d4dbafdb318..90e27458ddb7 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -512,7 +512,8 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
cma_sysfs_alloc_pages_count(cma, count);
} else {
count_vm_event(CMA_ALLOC_FAIL);
- cma_sysfs_fail_pages_count(cma, count);
+ if (cma)
+ cma_sysfs_fail_pages_count(cma, count);
}

return page;
--
2.30.2

2021-03-16 21:21:32

by Minchan Kim

Subject: Re: [PATCH] mm: cma: Fix potential null dereference on pointer cma

On Tue, Mar 16, 2021 at 10:04:33AM +0000, Colin King wrote:
> From: Colin Ian King <[email protected]>
>
> At the start of the function there is a null pointer check on cma
> and then branch to error handling label 'out'. The subsequent call
> to cma_sysfs_fail_pages_count dereferences cma, hence there is a
> potential null pointer deference issue. Fix this by only calling
> cma_sysfs_fail_pages_count if cma is not null.
>
> Addresses-Coverity: ("Dereference after null check")
> Fixes: dc4764f7e9ac ("mm: cma: support sysfs")
> Signed-off-by: Colin Ian King <[email protected]>
Acked-by: Minchan Kim <[email protected]>

2021-03-17 07:15:22

by John Hubbard

Subject: Re: [PATCH] mm: cma: Fix potential null dereference on pointer cma

On 3/16/21 3:04 AM, Colin King wrote:
> From: Colin Ian King <[email protected]>
>
> At the start of the function there is a null pointer check on cma
> and then branch to error handling label 'out'. The subsequent call
> to cma_sysfs_fail_pages_count dereferences cma, hence there is a
> potential null pointer deference issue. Fix this by only calling

As far as I can tell, it's not possible to actually cause that null
failure with the existing kernel code paths. *Might* be worth mentioning
that here (unless I'm wrong), but either way, looks good, so:

Reviewed-by: John Hubbard <[email protected]>

thanks,
--
John Hubbard
NVIDIA

> cma_sysfs_fail_pages_count if cma is not null.
>
> Addresses-Coverity: ("Dereference after null check")
> Fixes: dc4764f7e9ac ("mm: cma: support sysfs")
> Signed-off-by: Colin Ian King <[email protected]>
> ---
> mm/cma.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/cma.c b/mm/cma.c
> index 6d4dbafdb318..90e27458ddb7 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -512,7 +512,8 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
> cma_sysfs_alloc_pages_count(cma, count);
> } else {
> count_vm_event(CMA_ALLOC_FAIL);
> - cma_sysfs_fail_pages_count(cma, count);
> + if (cma)
> + cma_sysfs_fail_pages_count(cma, count);
> }
>
> return page;
>