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

[Weiming Shi]

Konstantin Komarov <almaz.alexandrovich@xxxxxxxxxxxxxxxxxxxx>
于2026年7月28日周二 17:54写道：
>
> 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 <xmei5@xxxxxxx>
> > Assisted-by: Claude:claude-opus-4-8
> > Signed-off-by: Weiming Shi <bestswngs@xxxxxxxxx>
> > ---
> >   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
>

Hi Konstantin,

Thank you for the update and for applying the patch.

Best regards,
Weiming Shi