[PATCH] mm: handle potential NULL return from anon_vma_name_reuse()

[Ye Liu <ye.liu@linux.dev>]

From: Ye Liu <liuye@kylinos.cn>

The anon_vma_name_reuse() function may return NULL if memory allocation
fails in anon_vma_name_alloc(). Currently, callers dup_anon_vma_name()
and replace_anon_vma_name() do not check the return value, which could
lead to NULL pointer dereferences.

This patch adds proper error handling:
- In dup_anon_vma_name(), if anon_vma_name_reuse() returns NULL, emit a
  warning via WARN_ON_ONCE(1) since this is an unexpected condition.
- In replace_anon_vma_name(), return -ENOMEM to propagate the allocation
  failure to the caller.

These changes improve robustness against memory allocation failures.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
---
 include/linux/mm_inline.h | 12 +++++++++---
 mm/madvise.c              |  7 ++++++-
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index a171070e15f0..9bbaf8287806 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -421,9 +421,15 @@ static inline void dup_anon_vma_name(struct vm_area_struct *orig_vma,
 				     struct vm_area_struct *new_vma)
 {
 	struct anon_vma_name *anon_name = anon_vma_name(orig_vma);
-
-	if (anon_name)
-		new_vma->anon_name = anon_vma_name_reuse(anon_name);
+	struct anon_vma_name *new_name;
+
+	if (anon_name) {
+		new_name = anon_vma_name_reuse(anon_name);
+		if (new_name)
+			new_vma->anon_name = new_name;
+		else
+			WARN_ON_ONCE(1);
+	}
 }
 
 static inline void free_anon_vma_name(struct vm_area_struct *vma)
diff --git a/mm/madvise.c b/mm/madvise.c
index 69708e953cf5..ccb937a37e70 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -118,6 +118,7 @@ static int replace_anon_vma_name(struct vm_area_struct *vma,
 				 struct anon_vma_name *anon_name)
 {
 	struct anon_vma_name *orig_name = anon_vma_name(vma);
+	struct anon_vma_name *new_name;
 
 	if (!anon_name) {
 		vma->anon_name = NULL;
@@ -128,7 +129,11 @@ static int replace_anon_vma_name(struct vm_area_struct *vma,
 	if (anon_vma_name_eq(orig_name, anon_name))
 		return 0;
 
-	vma->anon_name = anon_vma_name_reuse(anon_name);
+	new_name = anon_vma_name_reuse(anon_name);
+	if (!new_name)
+		return -ENOMEM;
+
+	vma->anon_name = new_name;
 	anon_vma_name_put(orig_name);
 
 	return 0;
-- 
2.43.0