[PATCH] erofs: stop parsing non-compact HEAD index if clusterofs is invalid

[Gao Xiang]

Syzbot generated a crafted image [1] with a non-compact HEAD index of
clusterofs 33024 while valid numbers should be 0 ~ lclustersize-1,
which causes the following unexpected behavior as below:

 BUG: unable to handle page fault for address: fffff52101a3fff9
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 23ffed067 P4D 23ffed067 PUD 0
 Oops: 0000 [#1] PREEMPT SMP KASAN
 CPU: 1 PID: 4398 Comm: kworker/u5:1 Not tainted 6.3.0-rc6-syzkaller-g09a9639e56c0 #0
 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/30/2023
 Workqueue: erofs_worker z_erofs_decompressqueue_work
 RIP: 0010:z_erofs_decompress_queue+0xb7e/0x2b40
 ...
 Call Trace:
  <TASK>
  z_erofs_decompressqueue_work+0x99/0xe0
  process_one_work+0x8f6/0x1170
  worker_thread+0xa63/0x1210
  kthread+0x270/0x300
  ret_from_fork+0x1f/0x30

Note that normal images or images using compact indexes are not
impacted.  Let's fix this now.

[1] https://lore.kernel.org/r/000000000000ec75b005ee97fbaa@google.com

Reported-by: syzbot+aafb3f37cfeb6534c4ac at syzkaller.appspotmail.com
Fixes: 02827e1796b3 ("staging: erofs: add erofs_map_blocks_iter")
Fixes: 152a333a5895 ("staging: erofs: add compacted compression indexes support")
Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
---
 fs/erofs/zmap.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index cbd3f72c83e9..7ca108c3834c 100644
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -85,6 +85,10 @@ static int legacy_load_cluster_from_disk(struct z_erofs_maprecorder *m,
 		if (advise & Z_EROFS_LI_PARTIAL_REF)
 			m->partialref = true;
 		m->clusterofs = le16_to_cpu(di->di_clusterofs);
+		if (m->clusterofs >= 1 << vi->z_logical_clusterbits) {
+			DBG_BUGON(1);
+			return -EFSCORRUPTED;
+		}
 		m->pblk = le32_to_cpu(di->di_u.blkaddr);
 		break;
 	default:
-- 
2.24.4