[PATCH] fs/ntfs3: bound attr_off in UpdateResidentValue against data_off

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

In do_action()'s UpdateResidentValue case (fslog.c:3307),
lrh->attr_off and lrh->redo_len come from the on-disk LRH.
When they satisfy aoff + dlen < attr->res.data_off, the
assignment

	attr->res.data_size = cpu_to_le32(aoff + dlen - data_off);

underflows to ~4 GiB (e.g. 0xFFFFFFF9 when aoff=0x10, dlen=1,
data_off=0x18).  Subsequent code that reads attr->res.data_size
to walk the resident attribute payload would then read up to
4 GiB past the 1024-byte MFT record allocation.

The existing mi_enum_attr() defense in fs/ntfs3/record.c:287
catches the corrupted data_size on the next attribute walk
and fails the mount, but only on the path that walks all
attributes.  A read site that picks an attribute by name and
reads its data_size without re-validating is not covered.
Validate aoff against data_off and asize at the source.

Reproduced under UML+KASAN on mainline 8d90b09e6741 via
pr_warn-only probe: with aoff=0x10 and data_off=0x18, the
post-assignment data_size is 0xfffffff9 (mount then fails
at -22 from mi_enum_attr).

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 | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/fs/ntfs3/fslog.c b/fs/ntfs3/fslog.c
index acfa18b84401e..4977ac1f62027 100644
--- a/fs/ntfs3/fslog.c
+++ b/fs/ntfs3/fslog.c
@@ -3325,6 +3325,17 @@ static int do_action(struct ntfs_log *log, struct OPEN_ATTR_ENRTY *oe,
 		nsize = ALIGN(nsize, 8);
 		data_off = le16_to_cpu(attr->res.data_off);
 
+		/*
+		 * aoff comes from the on-disk lrh->attr_off.  Forbid
+		 * writes that begin below the resident attribute's
+		 * data_off (which would overwrite the resident header),
+		 * and forbid aoff + dlen < data_off, which would make
+		 * the data_size assignment below underflow to ~4 GiB.
+		 */
+		if (aoff < data_off || aoff + dlen < data_off ||
+		    aoff + dlen > asize)
+			goto dirty_vol;
+
 		if (nsize < asize) {
 			memmove(Add2Ptr(attr, aoff), data, dlen);
 			data = NULL; // To skip below memmove().
-- 
2.53.0