[PATCH 1/5] mm: Trigger bug on if a section is not found in __section_nr

["Alastair D'Silva" <alastair@xxxxxxxxxxx>]

From: Alastair D'Silva <alastair@xxxxxxxxxxx>

If a memory section comes in where the physical address is greater than
that which is managed by the kernel, this function would not trigger the
bug and instead return a bogus section number.

This patch tracks whether the section was actually found, and triggers the
bug if not.

Signed-off-by: Alastair D'Silva <alastair@xxxxxxxxxxx>
---
 mm/sparse.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index fd13166949b5..104a79fedd00 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -105,20 +105,23 @@ static inline int sparse_index_init(unsigned long section_nr, int nid)
 int __section_nr(struct mem_section* ms)
 {
 	unsigned long root_nr;
-	struct mem_section *root = NULL;
+	struct mem_section *found = NULL;
+	struct mem_section *root;
 
 	for (root_nr = 0; root_nr < NR_SECTION_ROOTS; root_nr++) {
 		root = __nr_to_section(root_nr * SECTIONS_PER_ROOT);
 		if (!root)
 			continue;
 
-		if ((ms >= root) && (ms < (root + SECTIONS_PER_ROOT)))
-		     break;
+		if ((ms >= root) && (ms < (root + SECTIONS_PER_ROOT))) {
+			found = root;
+			break;
+		}
 	}
 
-	VM_BUG_ON(!root);
+	VM_BUG_ON(!found);
 
-	return (root_nr * SECTIONS_PER_ROOT) + (ms - root);
+	return (root_nr * SECTIONS_PER_ROOT) + (ms - found);
 }
 #else
 int __section_nr(struct mem_section* ms)
-- 
2.21.0