linux-kernel - [PATCH 1/1] mm/madvise: initialize prev pointer in madvise_walk

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Message-ID: <20250617020544.57305-1-lance.yang@linux.dev>
Date: Tue, 17 Jun 2025 10:05:43 +0800
From: Lance Yang <ioworker0@...il.com>
To: akpm@...ux-foundation.org
Cc: 21cnbao@...il.com,
	david@...hat.com,
	Liam.Howlett@...cle.com,
	vbabka@...e.cz,
	jannh@...gle.com,
	lorenzo.stoakes@...cle.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Lance Yang <lance.yang@...ux.dev>
Subject: [PATCH 1/1] mm/madvise: initialize prev pointer in madvise_walk_vmas

From: Lance Yang <lance.yang@...ux.dev>

The prev pointer was uninitialized, which could lead to undefined behavior
where its address is taken and passed to the visit() callback without being
assigned a value.

Initializing it to NULL makes the code safer and prevents potential bugs
if a future callback function attempts to read from it.

Signed-off-by: Lance Yang <lance.yang@...ux.dev>
---
 mm/madvise.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 267d8e4adf31..c87325000303 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1536,10 +1536,10 @@ int madvise_walk_vmas(struct mm_struct *mm, unsigned long start,
 				   struct vm_area_struct **prev, unsigned long start,
 				   unsigned long end, void *arg))
 {
+	struct vm_area_struct *prev = NULL;
 	struct vm_area_struct *vma;
-	struct vm_area_struct *prev;
-	unsigned long tmp;
 	int unmapped_error = 0;
+	unsigned long tmp;
 	int error;
 
 	/*
-- 
2.49.0