linux-kernel - Re: [syzbot] [mm?] WARNING in __folio_rmap_sanity

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Message-ID: <20241231084108.1146-1-hdanton@sina.com>
Date: Tue, 31 Dec 2024 16:41:06 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+c0673e1f1f054fac28c2@...kaller.appspotmail.com>
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] WARNING in __folio_rmap_sanity_checks (2)

On Fri, 27 Dec 2024 20:56:21 -0800
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    8155b4ef3466 Add linux-next specific files for 20241220
> git tree:       linux-next
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1652fadf980000

#syz test

--- x/mm/filemap.c
+++ y/mm/filemap.c
@@ -3636,6 +3636,10 @@ static vm_fault_t filemap_map_folio_rang
 		continue;
 skip:
 		if (count) {
+			for (unsigned int i = 0; i < count; i++) {
+				if (page_folio(page + i) != folio)
+					goto out;
+			}
 			set_pte_range(vmf, folio, page, count, addr);
 			*rss += count;
 			folio_ref_add(folio, count);
@@ -3658,6 +3662,7 @@ skip:
 			ret = VM_FAULT_NOPAGE;
 	}
 
+out:
 	vmf->pte = old_ptep;
 
 	return ret;
@@ -3702,7 +3707,7 @@ vm_fault_t filemap_map_pages(struct vm_f
 	struct file *file = vma->vm_file;
 	struct address_space *mapping = file->f_mapping;
 	pgoff_t file_end, last_pgoff = start_pgoff;
-	unsigned long addr;
+	unsigned long addr, pmd_end;
 	XA_STATE(xas, &mapping->i_pages, start_pgoff);
 	struct folio *folio;
 	vm_fault_t ret = 0;
@@ -3731,6 +3736,12 @@ vm_fault_t filemap_map_pages(struct vm_f
 	if (end_pgoff > file_end)
 		end_pgoff = file_end;
 
+	/* make vmf->pte[x] valid */
+	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;
--