[PATCH] fs/ntfs3: fix out-of-bounds read in read_log_rec_buf()

[Weiming Shi <bestswngs@gmail.com>]

read_log_rec_buf() copies a log record into a caller buffer starting at

	u32 off = lsn_to_page_off(log, lsn) + log->record_header_len;

log->record_header_len (and log->data_off, used for the following pages)
comes verbatim from the on-disk restart area and is only checked for
8-byte alignment in is_rst_area_valid(), so off can exceed
log->page_size. "tail = log->page_size - off" then underflows and
memcpy() reads past the page_size-sized buffer returned by
read_log_page(), spilling adjacent slab memory into the replay buffer.

This is reachable by mounting a crafted NTFS image:

 BUG: KASAN: slab-out-of-bounds in read_log_rec_buf+0x216/0x580
 Read of size 64 at addr ffff88800a877ff8 by task exploit/127
  read_log_rec_buf fs/ntfs3/fslog.c:2299
  log_replay fs/ntfs3/fslog.c:4216
  ntfs_loadlog_and_replay fs/ntfs3/fsntfs.c:324
  ntfs_fill_super fs/ntfs3/super.c:1392
  get_tree_bdev_flags fs/super.c:1694
  __x64_sys_mount fs/namespace.c:4360
 The buggy address is located 4088 bytes to the right of
 the 4096-byte region [ffff88800a876000, ffff88800a877000)

Reject an in-page offset outside the current page before the copy.

Fixes: b46acd6a6a62 ("fs/ntfs3: Add NTFS journal")
Assisted-by: Claude:claude-opus-4-8
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
---
 fs/ntfs3/fslog.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/ntfs3/fslog.c b/fs/ntfs3/fslog.c
index f038c799e7ac..ee413dc80d3a 100644
--- a/fs/ntfs3/fslog.c
+++ b/fs/ntfs3/fslog.c
@@ -2276,7 +2276,15 @@ static int read_log_rec_buf(struct ntfs_log *log,
 	 */
 	for (;;) {
 		bool usa_error;
-		u32 tail = log->page_size - off;
+		u32 tail;
+
+		/* off comes from the on-disk restart area; bound it. */
+		if (off >= log->page_size) {
+			err = -EINVAL;
+			goto out;
+		}
+
+		tail = log->page_size - off;
 
 		if (tail >= data_len)
 			tail = data_len;
-- 
2.43.0