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SubjectRe: [PATCH] mm: cma: Fix potential null dereference on pointer cma
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On 3/16/21 3:04 AM, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
>
> 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 <jhubbard@nvidia.com>

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 <colin.king@canonical.com>
> ---
> 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;
>

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