[PATCH] fs/ntfs3: reject an oversized resident attribute on the inline iomap path

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

attr_data_get_block_locked() maps a resident attribute as an IOMAP_INLINE
extent using the resident value length taken straight from the on-disk
attribute, without checking that it fits within the single page that backs
an inline extent.  mi_enum_attr() only bounds that length against the MFT
record size, so a corrupted volume with MFT records larger than a page can
present a resident $DATA whose length exceeds PAGE_SIZE; on a buffered
write the inline extent then fails the page-fit invariant and
iomap_write_end_inline() trips BUG_ON(!iomap_inline_data_valid()).

Impact: writing to a resident file on a mounted crafted NTFS volume whose
MFT records are larger than a page oopses the kernel at
fs/iomap/buffered-io.c:1061.

Reject such an attribute in attr_data_get_block_locked(), before the inline
buffer is allocated and the size reaches the iomap core.

Fixes: 099ef9ab9203 ("fs/ntfs3: implement iomap-based file operations")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---

The oops on current mainline (the inline buffer is kmemdup()ed), reproduced
on 7.1.0-rc4 with KASAN by writing to a resident file on a crafted volume
whose resident $DATA value length exceeds PAGE_SIZE (reachable only with MFT
records >= 8 KiB):

  kernel BUG at fs/iomap/buffered-io.c:1061!
  RIP: 0010:iomap_write_end+0x48e/0x5c0
   iomap_file_buffered_write
   ntfs_file_write_iter
   vfs_write

This also matters for the queued "ntfs3: Allocate iomap inline_data using
alloc_page" change: there the same oversized data_size makes
memcpy(page_address(page), resident_data(attr_b), data_size) write past the
single alloc_page() page.  Bounding data_size here prevents both.

With this patch the offending write returns -EINVAL; normal resident and
non-resident writes are unaffected.

 fs/ntfs3/attrib.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/ntfs3/attrib.c b/fs/ntfs3/attrib.c
index e61c5bf7e27e4..d41ca930daebc 100644
--- a/fs/ntfs3/attrib.c
+++ b/fs/ntfs3/attrib.c
@@ -1039,6 +1039,21 @@ int attr_data_get_block_locked(struct ntfs_inode *ni, CLST vcn, CLST clen,
 
 	if (!attr_b->non_res) {
 		u32 data_size = le32_to_cpu(attr_b->res.data_size);
+
+		/*
+		 * A resident attribute is mapped as an IOMAP_INLINE extent,
+		 * which must fit within a single page: iomap_write_end_inline()
+		 * asserts iomap_inline_data_valid(), and the inline buffer is a
+		 * single page.  mi_enum_attr() only bounds the resident value
+		 * length against the MFT record size, so a corrupted volume with
+		 * records larger than a page can report data_size > PAGE_SIZE.
+		 * Reject it here, before it overflows the inline page or trips
+		 * the iomap BUG_ON.
+		 */
+		if (data_size > PAGE_SIZE) {
+			err = -EINVAL;
+			goto out;
+		}
 		*lcn = RESIDENT_LCN;
 		*len = data_size;
 		if (res && data_size) {
-- 
2.53.0