[PATCH] fs/ntfs3: bound NTFS_DE view.data_off in UpdateRecordData{Root,Allocation}

[Michael Bommarito <michael.bommarito@gmail.com>]

In do_action()'s UpdateRecordDataRoot (fslog.c:3489) and
UpdateRecordDataAllocation (fslog.c:3697) cases, the memmove
destination is `Add2Ptr(e, le16_to_cpu(e->view.data_off))`,
where e->view.data_off comes from an on-disk NTFS_DE inside
an INDEX_ROOT or INDEX_BUFFER.  Neither case validates
view.data_off + dlen against e->size; the existing
check_if_index_root / check_if_alloc_index helpers walk the
entry chain and validate the entry's offset, but not its
internal view fields.

The neighbouring read sites (e.g., fs/ntfs3/index.c when
iterating view entries) check view.data_off + view.data_size
<= e->size.  Apply the same bound at the two memmove sites.

Reproduced under UML+KASAN on mainline 8d90b09e6741 via
pr_warn-only probe instrumentation: with view.data_off forced
to 0xFFFC, the memmove writes 32 bytes past the end of the
NTFS_DE.

This is similar in shape to Pavitra Jha's 2026-05-02 patch
"fs/ntfs3: prevent oob in case UpdateRecordDataRoot"
(<20260502105008.21827-1-jhapavitra98@gmail.com>) which
proposes calling ntfs3_bad_de_range(); that helper does not
exist in mainline.  This patch uses inline checks.

Fixes: b46acd6a6a62 ("fs/ntfs3: Add NTFS journal")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---
 fs/ntfs3/fslog.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/fs/ntfs3/fslog.c b/fs/ntfs3/fslog.c
index acfa18b84401e..127860fd2ab50 100644
--- a/fs/ntfs3/fslog.c
+++ b/fs/ntfs3/fslog.c
@@ -3497,6 +3497,18 @@ static int do_action(struct ntfs_log *log, struct OPEN_ATTR_ENRTY *oe,
 
 		e = Add2Ptr(attr, le16_to_cpu(lrh->attr_off));
 
+		/*
+		 * e->view.data_off and dlen come from the on-disk
+		 * INDEX_ROOT entry / LRH.  The neighbouring read sites
+		 * (e.g. fs/ntfs3/index.c) check that
+		 * view.data_off + view.data_size <= e->size; mirror that
+		 * bound here so the memmove cannot reach past the entry.
+		 */
+		if (le16_to_cpu(e->view.data_off) > le16_to_cpu(e->size) ||
+		    le16_to_cpu(e->view.data_off) + dlen >
+			    le16_to_cpu(e->size))
+			goto dirty_vol;
+
 		memmove(Add2Ptr(e, le16_to_cpu(e->view.data_off)), data, dlen);
 
 		mi->dirty = true;
@@ -3689,6 +3701,12 @@ static int do_action(struct ntfs_log *log, struct OPEN_ATTR_ENRTY *oe,
 			goto dirty_vol;
 		}
 
+		/* See UpdateRecordDataRoot for the rationale. */
+		if (le16_to_cpu(e->view.data_off) > le16_to_cpu(e->size) ||
+		    le16_to_cpu(e->view.data_off) + dlen >
+			    le16_to_cpu(e->size))
+			goto dirty_vol;
+
 		memmove(Add2Ptr(e, le16_to_cpu(e->view.data_off)), data, dlen);
 
 		a_dirty = true;
-- 
2.53.0