[PATCH 6.6.y 2/2] erofs: unify lcn as u64 for 32-bit platforms

[Artem Dinaburg <artem@trailofbits.com>]

From: Gao Xiang <hsiangkao@linux.alibaba.com>

[ Upstream commit 2d8c7edcb661812249469f4a5b62e9339118846f ]

As sashiko reported [1], `lcn` was typed as `unsigned long` (or
`unsigned int` sometimes), which is only 32 bits wide on 32-bit
platforms, which causes `(lcn << lclusterbits)` to be truncated
at 4 GiB.

In order to consolidate the logic, just use `u64` consistently
around the codebase.

[1] https://sashiko.dev/r/20260420034612.1899973-1-hsiangkao%40linux.alibaba.com

[ Backport to 6.6.y: rebase after the CVE-2025-68251 compact-index
  validation change. Widen its new lcn diagnostic along with the
  recorder, full and compact loader data flow, lookback and compressed-
  length locals to u64. ]

Fixes: 152a333a5895 ("staging: erofs: add compacted compression indexes support")
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Assisted-by: LLM
Signed-off-by: Artem Dinaburg <artem@trailofbits.com>
---
This is patch 2 of 2 in the ordered 6.6.y backport series.
This change addresses CVE-2026-53015. The EROFS zmap implementation and the
preceding compact-index validation fix otherwise retain 32-bit lcn values
in shifts on 32-bit systems; widening the complete data flow and the
validation diagnostic to u64 prevents 4-GiB truncation without weakening
the new loop check.
This needed a target-specific adjustment; I called it out in the bracketed
backport note above.

The fix is absent from the pinned 6.6.y branch and queue and must follow
CVE-2025-68251 in this series.

 fs/erofs/zmap.c | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index e53d5239f04d..990322b228cb 100644
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -12,7 +12,7 @@ struct z_erofs_maprecorder {
 	struct erofs_map_blocks *map;
 	void *kaddr;
 
-	unsigned long lcn;
+	u64 lcn;
 	/* compression extent information gathered */
 	u8  type, headtype;
 	u16 clusterofs;
@@ -22,8 +22,7 @@ struct z_erofs_maprecorder {
 	bool partialref;
 };
 
-static int z_erofs_load_full_lcluster(struct z_erofs_maprecorder *m,
-				      unsigned long lcn)
+static int z_erofs_load_full_lcluster(struct z_erofs_maprecorder *m, u64 lcn)
 {
 	struct inode *const inode = m->inode;
 	struct erofs_inode *const vi = EROFS_I(inode);
@@ -219,7 +218,7 @@ static int unpack_compacted_index(struct z_erofs_maprecorder *m,
 }
 
 static int z_erofs_load_compact_lcluster(struct z_erofs_maprecorder *m,
-					 unsigned long lcn, bool lookahead)
+					 u64 lcn, bool lookahead)
 {
 	struct inode *const inode = m->inode;
 	struct erofs_inode *const vi = EROFS_I(inode);
@@ -270,7 +269,7 @@ 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)
+					   u64 lcn, bool lookahead)
 {
 	struct erofs_inode *vi = EROFS_I(m->inode);
 	int err;
@@ -289,7 +288,7 @@ static int z_erofs_load_lcluster_from_disk(struct z_erofs_maprecorder *m,
 		return err;
 
 	if (m->type >= Z_EROFS_LCLUSTER_TYPE_MAX) {
-		erofs_err(m->inode->i_sb, "unknown type %u @ lcn %u of nid %llu",
+		erofs_err(m->inode->i_sb, "unknown type %u @ lcn %llu of nid %llu",
 			  m->type, lcn, vi->nid);
 		DBG_BUGON(1);
 		return -EOPNOTSUPP;
@@ -310,7 +309,7 @@ static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
 	const unsigned int lclusterbits = vi->z_logical_clusterbits;
 
 	while (m->lcn >= lookback_distance) {
-		unsigned long lcn = m->lcn - lookback_distance;
+		u64 lcn = m->lcn - lookback_distance;
 		int err;
 
 		err = z_erofs_load_lcluster_from_disk(m, lcn, false);
@@ -330,14 +329,14 @@ static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
 			m->map->m_la = (lcn << lclusterbits) | m->clusterofs;
 			return 0;
 		default:
-			erofs_err(sb, "unknown type %u @ lcn %lu of nid %llu",
+			erofs_err(sb, "unknown type %u @ lcn %llu of nid %llu",
 				  m->type, lcn, vi->nid);
 			DBG_BUGON(1);
 			return -EOPNOTSUPP;
 		}
 	}
 err_bogus:
-	erofs_err(sb, "bogus lookback distance %u @ lcn %lu of nid %llu",
+	erofs_err(sb, "bogus lookback distance %u @ lcn %llu of nid %llu",
 		  lookback_distance, m->lcn, vi->nid);
 	DBG_BUGON(1);
 	return -EFSCORRUPTED;
@@ -350,7 +349,7 @@ static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m,
 	struct erofs_inode *const vi = EROFS_I(m->inode);
 	struct erofs_map_blocks *const map = m->map;
 	const unsigned int lclusterbits = vi->z_logical_clusterbits;
-	unsigned long lcn;
+	u64 lcn;
 	int err;
 
 	DBG_BUGON(m->type != Z_EROFS_LCLUSTER_TYPE_PLAIN &&
@@ -402,7 +401,7 @@ static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m,
 			break;
 		fallthrough;
 	default:
-		erofs_err(sb, "cannot found CBLKCNT @ lcn %lu of nid %llu", lcn,
+		erofs_err(sb, "cannot found CBLKCNT @ lcn %llu of nid %llu", lcn,
 			  vi->nid);
 		DBG_BUGON(1);
 		return -EFSCORRUPTED;
@@ -411,7 +410,7 @@ static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m,
 	map->m_plen = erofs_pos(sb, m->compressedblks);
 	return 0;
 err_bonus_cblkcnt:
-	erofs_err(sb, "bogus CBLKCNT @ lcn %lu of nid %llu", lcn, vi->nid);
+	erofs_err(sb, "bogus CBLKCNT @ lcn %llu of nid %llu", lcn, vi->nid);
 	DBG_BUGON(1);
 	return -EFSCORRUPTED;
 }
-- 
2.39.5