[PATCH] fs/ntfs3: reject restart table growth beyond U16_MAX entries

During $LogFile replay, log_replay() indexes the transaction table by the
transact_id taken from the log record header.  check_log_rec() only
verifies that transact_id is non-zero and properly aligned, not its
magnitude, so a crafted image can request an arbitrarily large index.

alloc_rsttbl_from_idx() grows the table to cover that index via
extend_rsttbl(), which passes the new entry count to init_rsttbl():

	rt = init_rsttbl(esize, used + add);

used + add is computed as u32 but init_rsttbl() takes a u16, and the
count is stored in struct RESTART_TABLE as a __le16.  When used + add
exceeds U16_MAX it is truncated, init_rsttbl() allocates a table far
smaller than the index requires, and alloc_rsttbl_from_idx() then
dereferences and writes at the original, untruncated offset -- an
out-of-bounds access past the allocation, reachable by mounting a
crafted NTFS image.

 BUG: KASAN: use-after-free in alloc_rsttbl_from_idx (fs/ntfs3/fslog.c:950)
 Read of size 4 at addr ffff8880327ffff8 by task exploit
  alloc_rsttbl_from_idx (fs/ntfs3/fslog.c:950)
  log_replay (fs/ntfs3/fslog.c:4562)
  ntfs_loadlog_and_replay (fs/ntfs3/fsntfs.c:324)
  ntfs_fill_super (fs/ntfs3/super.c:1393)
  get_tree_bdev_flags
  vfs_get_tree
  path_mount
  __x64_sys_mount

A restart table is limited to U16_MAX entries by its __le16 count, so a
larger growth request is invalid input.  Reject it in extend_rsttbl();
all callers already handle a NULL return.

Fixes: b46acd6a6a62 ("fs/ntfs3: Add NTFS journal")
Reported-by: Xiang Mei <[email protected]>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Weiming Shi <[email protected]>
---
 fs/ntfs3/fslog.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ntfs3/fslog.c b/fs/ntfs3/fslog.c
index f038c799e7ac..78f34442aaaa 100644
--- a/fs/ntfs3/fslog.c
+++ b/fs/ntfs3/fslog.c
@@ -853,6 +853,9 @@ static inline struct RESTART_TABLE *extend_rsttbl(struct RESTART_TABLE *tbl,
 	u32 used = le16_to_cpu(tbl->used);
 	struct RESTART_TABLE *rt;
 
+	if (used + add > U16_MAX)
+		return NULL;
+
 	rt = init_rsttbl(esize, used + add);
 	if (!rt)
 		return NULL;
-- 
2.43.0