slab: Mark large folios for debugging purposes

If a user calls p = kmalloc(1024); kfree(p); kfree(p); and 'p' was the
only object in the slab, we may free the slab after the first call to
kfree().  If we do, we clear PGTY_slab and the second call to kfree()
will call free_large_kmalloc().  That will leave a trace in the logs
("object pointer: 0x%p"), but otherwise proceed to free the memory,
which is likely to corrupt the page allocator's metadata.

Allocate a new page type for large kmalloc and mark the memory with it
while it's allocated.  That lets us detect this double-free and return
without harming any data structures.

Reported-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

1 files changed, 7 insertions, 0 deletions

diff --git a/mm/slub.c b/mm/slub.c
index d94af020b305..3e6ab4986f8f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4255,6 +4255,7 @@ static void *___kmalloc_large_node(size_t size, gfp_t flags, int node)
 		ptr = folio_address(folio);
 		lruvec_stat_mod_folio(folio, NR_SLAB_UNRECLAIMABLE_B,
 				      PAGE_SIZE << order);
+		__folio_set_large_kmalloc(folio);
 	}
 
 	ptr = kasan_kmalloc_large(ptr, size, flags);
@@ -4730,6 +4731,11 @@ static void free_large_kmalloc(struct folio *folio, void *object)
 {
 	unsigned int order = folio_order(folio);
 
+	if (WARN_ON_ONCE(!folio_test_large_kmalloc(folio))) {
+		dump_page(&folio->page, "Not a kmalloc allocation");
+		return;
+	}
+
 	if (WARN_ON_ONCE(order == 0))
 		pr_warn_once("object pointer: 0x%p\n", object);
 
@@ -4739,6 +4745,7 @@ static void free_large_kmalloc(struct folio *folio, void *object)
 
 	lruvec_stat_mod_folio(folio, NR_SLAB_UNRECLAIMABLE_B,
 			      -(PAGE_SIZE << order));
+	__folio_clear_large_kmalloc(folio);
 	folio_put(folio);
 }