[PATCH] filemap: Init the newly allocated folio memory to 0 for the filemap

[Lizhi Xu]

syzbot report KMSAN: uninit-value in pick_link, this is because the
corresponding folio was not found from the mapping, and the memory was
not initialized when allocating a new folio for the filemap.

To avoid the occurrence of kmsan report uninit-value, initialize the
newly allocated folio memory to 0.

Reported-and-tested-by: syzbot+24ac24ff58dc5b0d26b9@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=24ac24ff58dc5b0d26b9
Signed-off-by: Lizhi Xu <lizhi.xu@xxxxxxxxxxxxx>
---
 mm/filemap.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c
index 657bcd887fdb..1b22eab691e8 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3753,6 +3753,11 @@ static struct folio *do_read_cache_folio(struct address_space *mapping,
 		folio = filemap_alloc_folio(gfp, 0);
 		if (!folio)
 			return ERR_PTR(-ENOMEM);
+
+		void *kaddr = kmap_local_folio(folio, 0);
+		memset(kaddr, 0, folio_size(folio));
+		kunmap_local(kaddr);
+
 		err = filemap_add_folio(mapping, folio, index, gfp);
 		if (unlikely(err)) {
 			folio_put(folio);
-- 
2.43.0