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

On 6/23/26 12:14, Weiming Shi wrote:

> 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
>
Hello,

Sorry for the delay.
Your patch was applied, thank you.

Regards,
Konstantin