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

[Colin King]

From: Colin Ian King <colin.k...@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
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.k...@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;
-- 
2.30.2