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

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Date:   Tue, 16 Mar 2021 10:04:33 +0000
From:   Colin King <colin.king@...onical.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Minchan Kim <minchan@...nel.org>,
        John Hubbard <jhubbard@...dia.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-mm@...ck.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] mm: cma: Fix potential null dereference on pointer cma

From: Colin Ian King <colin.king@...onical.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.king@...onical.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