[PATCH v3 1/1] check that order of free pages falls within valid range

[Alexander Egorenkov <egorenar@linux.ibm.com>]

This change makes __exclude_unnecessary_pages() more robust by
verifying that the order of a free page is valid before computing the size
of its memory block in the buddy system.

The order of a free page cannot be larger than (MAX_ORDER - 1) because
the array 'zone.free_area' is of size MAX_ORDER.

This situation is reproducible with some s390x dumps:

__exclude_unnecessary_pages: Invalid free page order: pfn=2690c0, order=52, max order=8

References:
- https://listman.redhat.com/archives/crash-utility/2021-September/009204.html
- https://www.kernel.org/doc/gorman/html/understand/understand009.html

Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
---
 makedumpfile.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/makedumpfile.c b/makedumpfile.c
index 2ef345879524..a6c2a4934ff9 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -6457,6 +6457,11 @@ __exclude_unnecessary_pages(unsigned long mem_map,
 		else if ((info->dump_level & DL_EXCLUDE_FREE)
 		    && info->page_is_buddy
 		    && info->page_is_buddy(flags, _mapcount, private, _count)) {
+			if (private >= ARRAY_LENGTH(zone.free_area)) {
+				MSG("WARNING: Invalid free page order: pfn=%llx, order=%lu, max order=%lu\n",
+				    pfn, private, ARRAY_LENGTH(zone.free_area) - 1);
+				continue;
+			}
 			nr_pages = 1 << private;
 			pfn_counter = &pfn_free;
 		}
-- 
2.34.1