linux-kernel - [PATCH 1/2] erofs: avoid infinite loops due to corrupted subpage compact indexes

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Message-ID: <20251017070539.901367-1-hsiangkao@linux.alibaba.com>
Date: Fri, 17 Oct 2025 15:05:38 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: linux-erofs@...ts.ozlabs.org
Cc: LKML <linux-kernel@...r.kernel.org>,
	Gao Xiang <hsiangkao@...ux.alibaba.com>,
	Robert Morris <rtm@...il.mit.edu>
Subject: [PATCH 1/2] erofs: avoid infinite loops due to corrupted subpage compact indexes

Robert reported an infinite loop observed by two crafted images.

The root cause is that `clusterofs` can be larger than `lclustersize`
for !NONHEAD `lclusters` in corrupted subpage compact indexes, e.g.:

  blocksize = lclustersize = 512   lcn = 6   clusterofs = 515

Move the corresponding check for full compress indexes to
`z_erofs_load_lcluster_from_disk()` to also cover subpage compact
compress indexes.

It also fixes the position of `m->type >= Z_EROFS_LCLUSTER_TYPE_MAX`
check, since it should be placed right after
`z_erofs_load_{compact,full}_lcluster()`.

Fixes: 8d2517aaeea3 ("erofs: fix up compacted indexes for block size < 4096")
Fixes: 1a5223c182fd ("erofs: do sanity check on m->type in z_erofs_load_compact_lcluster()")
Reported-by: Robert Morris <rtm@...il.mit.edu>
Closes: https://lore.kernel.org/r/35167.1760645886@localhost
Signed-off-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
---
 fs/erofs/zmap.c | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index e5581dbeb4c2..6aca228cd2a5 100644
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -55,10 +55,6 @@ static int z_erofs_load_full_lcluster(struct z_erofs_maprecorder *m,
 	} else {
 		m->partialref = !!(advise & Z_EROFS_LI_PARTIAL_REF);
 		m->clusterofs = le16_to_cpu(di->di_clusterofs);
-		if (m->clusterofs >= 1 << vi->z_lclusterbits) {
-			DBG_BUGON(1);
-			return -EFSCORRUPTED;
-		}
 		m->pblk = le32_to_cpu(di->di_u.blkaddr);
 	}
 	return 0;
@@ -240,21 +236,29 @@ static int z_erofs_load_compact_lcluster(struct z_erofs_maprecorder *m,
 static int z_erofs_load_lcluster_from_disk(struct z_erofs_maprecorder *m,
 					   unsigned int lcn, bool lookahead)
 {
+	struct erofs_inode *vi = EROFS_I(m->inode);
+	int err;
+
+	if (vi->datalayout == EROFS_INODE_COMPRESSED_COMPACT) {
+		err = z_erofs_load_compact_lcluster(m, lcn, lookahead);
+	} else {
+		DBG_BUGON(vi->datalayout != EROFS_INODE_COMPRESSED_FULL);
+		err = z_erofs_load_full_lcluster(m, lcn);
+	}
+	if (err)
+		return err;
+
 	if (m->type >= Z_EROFS_LCLUSTER_TYPE_MAX) {
 		erofs_err(m->inode->i_sb, "unknown type %u @ lcn %u of nid %llu",
-				m->type, lcn, EROFS_I(m->inode)->nid);
+			  m->type, lcn, EROFS_I(m->inode)->nid);
 		DBG_BUGON(1);
 		return -EOPNOTSUPP;
+	} else if (m->type != Z_EROFS_LCLUSTER_TYPE_NONHEAD &&
+		   m->clusterofs >= (1 << vi->z_lclusterbits)) {
+		DBG_BUGON(1);
+		return -EFSCORRUPTED;
 	}
-
-	switch (EROFS_I(m->inode)->datalayout) {
-	case EROFS_INODE_COMPRESSED_FULL:
-		return z_erofs_load_full_lcluster(m, lcn);
-	case EROFS_INODE_COMPRESSED_COMPACT:
-		return z_erofs_load_compact_lcluster(m, lcn, lookahead);
-	default:
-		return -EINVAL;
-	}
+	return 0;
 }
 
 static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
-- 
2.43.5