[PATCH v2] lib/iov_iter: fix to increase non slab folio refcount

[Sheng Yong]

From: Sheng Yong <shengyong1@xxxxxxxxxx>

When testing EROFS file-backed mount over v9fs on qemu, I encountered
a folio UAF issue. The page sanity check reports the following call
trace. The root cause is that pages in bvec are coalesced across a folio
bounary. The refcount of all non-slab folios should be increased to
ensure p9_releas_pages can put them correctly.

BUG: Bad page state in process md5sum  pfn:18300
page: refcount:0 mapcount:0 mapping:00000000d5ad8e4e index:0x60 pfn:0x18300
head: order:0 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
aops:z_erofs_aops ino:30b0f dentry name(?):"GoogleExtServicesCn.apk"
flags: 0x100000000000041(locked|head|node=0|zone=1)
raw: 0100000000000041 dead000000000100 dead000000000122 ffff888014b13bd0
raw: 0000000000000060 0000000000000020 00000000ffffffff 0000000000000000
head: 0100000000000041 dead000000000100 dead000000000122 ffff888014b13bd0
head: 0000000000000060 0000000000000020 00000000ffffffff 0000000000000000
head: 0100000000000000 0000000000000000 ffffffffffffffff 0000000000000000
head: 0000000000000010 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
Call Trace:
 dump_stack_lvl+0x53/0x70
 bad_page+0xd4/0x220
 __free_pages_ok+0x76d/0xf30
 __folio_put+0x230/0x320
 p9_release_pages+0x179/0x1f0
 p9_virtio_zc_request+0xa2a/0x1230
 p9_client_zc_rpc.constprop.0+0x247/0x700
 p9_client_read_once+0x34d/0x810
 p9_client_read+0xf3/0x150
 v9fs_issue_read+0x111/0x360
 netfs_unbuffered_read_iter_locked+0x927/0x1390
 netfs_unbuffered_read_iter+0xa2/0xe0
 vfs_iocb_iter_read+0x2c7/0x460
 erofs_fileio_rq_submit+0x46b/0x5b0
 z_erofs_runqueue+0x1203/0x21e0
 z_erofs_readahead+0x579/0x8b0
 read_pages+0x19f/0xa70
 page_cache_ra_order+0x4ad/0xb80
 filemap_readahead.isra.0+0xe7/0x150
 filemap_get_pages+0x7aa/0x1890
 filemap_read+0x320/0xc80
 vfs_read+0x6c6/0xa30
 ksys_read+0xf9/0x1c0
 do_syscall_64+0x9e/0x1a0
 entry_SYSCALL_64_after_hwframe+0x71/0x79

Fixes: b9c0e49abfca ("mm: decline to manipulate the refcount on a slab page")
Signed-off-by: Sheng Yong <shengyong1@xxxxxxxxxx>
---
 lib/iov_iter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
v2:
  * update commit message
  * update coding style

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 8c7fdb7d8c8f..bc9391e55d57 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1191,7 +1191,7 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
 			return -ENOMEM;
 		p = *pages;
 		for (int k = 0; k < n; k++) {
-			struct folio *folio = page_folio(page);
+			struct folio *folio = page_folio(page + k);
 			p[k] = page + k;
 			if (!folio_test_slab(folio))
 				folio_get(folio);
-- 
2.43.0