Re: [syzbot] [mm?] [xfs?] KASAN: slab-use-after-free Read in filemap_map_pages

[Hillf Danton]

On Tue, 31 Dec 2024 20:06:28 -0800
> syzbot found the following issue on:
> 
> HEAD commit:    8155b4ef3466 Add linux-next specific files for 20241220
> git tree:       linux-next
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17ed90b0580000

#syz test

--- x/mm/filemap.c
+++ y/mm/filemap.c
@@ -3703,6 +3703,7 @@ vm_fault_t filemap_map_pages(struct vm_f
 	struct address_space *mapping = file->f_mapping;
 	pgoff_t file_end, last_pgoff = start_pgoff;
 	unsigned long addr;
+	unsigned long pmd_end;
 	XA_STATE(xas, &mapping->i_pages, start_pgoff);
 	struct folio *folio;
 	vm_fault_t ret = 0;
@@ -3731,6 +3732,11 @@ vm_fault_t filemap_map_pages(struct vm_f
 	if (end_pgoff > file_end)
 		end_pgoff = file_end;
 
+	pmd_end = ALIGN(addr, PMD_SIZE);
+	pmd_end = (pmd_end - addr) >> PAGE_SHIFT;
+	if (end_pgoff - start_pgoff > pmd_end)
+		end_pgoff = start_pgoff + pmd_end;
+
 	folio_type = mm_counter_file(folio);
 	do {
 		unsigned long end;
--