Re: [PATCH v5] ocfs2: fix use-after-free in ocfs2_fault() when VM_FAULT_RETRY

[Tejas Bharambe]

Noted sir. Sending in v6


On Fri, Apr 10, 2026 at 1:30 AM Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx> wrote:
>
>
>
> On 4/10/26 4:04 PM, Tejas Bharambe wrote:
> > From: Tejas Bharambe <tejas.bharambe@xxxxxxxxxxx>
> >
> > filemap_fault() may drop the mmap_lock before returning VM_FAULT_RETRY,
> > as documented in mm/filemap.c:
> >
> >   "If our return value has VM_FAULT_RETRY set, it's because the mmap_lock
> >   may be dropped before doing I/O or by lock_folio_maybe_drop_mmap()."
> >
> > When this happens, a concurrent munmap() can call remove_vma() and free
> > the vm_area_struct via RCU. The saved 'vma' pointer in ocfs2_fault() then
> > becomes a dangling pointer, and the subsequent trace_ocfs2_fault() call
> > dereferences it -- a use-after-free.
> >
> > Fix this by saving the inode reference before calling filemap_fault(),
> > and removing vma from the trace event. The inode remains valid across
> > the lock drop since the file is still open, so the trace can fire in
> > all cases without dereferencing the potentially freed vma.
> >
>
> The commit log should also be updated.
> Also do not send to stable@xxxxxxxxxxxxxxx by default.
>
> Thanks,
> Joseph
>
> > Reported-by: syzbot+a49010a0e8fcdeea075f@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Closes: https://syzkaller.appspot.com/bug?extid=a49010a0e8fcdeea075f
> > Cc: stable@xxxxxxxxxxxxxxx
> > Suggested-by: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
> > Signed-off-by: Tejas Bharambe <tejas.bharambe@xxxxxxxxxxx>
> > ---
> >  fs/ocfs2/mmap.c        |  7 +++----
> >  fs/ocfs2/ocfs2_trace.h | 10 ++++------
> >  2 files changed, 7 insertions(+), 10 deletions(-)
> >
> > diff --git a/fs/ocfs2/mmap.c b/fs/ocfs2/mmap.c
> > index 50e2faf64c..6c570157ca 100644
> > --- a/fs/ocfs2/mmap.c
> > +++ b/fs/ocfs2/mmap.c
> > @@ -30,7 +30,8 @@
> >
> >  static vm_fault_t ocfs2_fault(struct vm_fault *vmf)
> >  {
> > -     struct vm_area_struct *vma = vmf->vma;
> > +     unsigned long long ip_blkno =
> > +             OCFS2_I(file_inode(vmf->vma->vm_file))->ip_blkno;
> >       sigset_t oldset;
> >       vm_fault_t ret;
> >
> > @@ -38,11 +39,9 @@ static vm_fault_t ocfs2_fault(struct vm_fault *vmf)
> >       ret = filemap_fault(vmf);
> >       ocfs2_unblock_signals(&oldset);
> >
> > -     trace_ocfs2_fault(OCFS2_I(vma->vm_file->f_mapping->host)->ip_blkno,
> > -                       vma, vmf->page, vmf->pgoff);
> > +     trace_ocfs2_fault(ip_blkno, vmf->page, vmf->pgoff);
> >       return ret;
> >  }
> > -
> >  static vm_fault_t __ocfs2_page_mkwrite(struct file *file,
> >                       struct buffer_head *di_bh, struct folio *folio)
> >  {
> > diff --git a/fs/ocfs2/ocfs2_trace.h b/fs/ocfs2/ocfs2_trace.h
> > index 4b32fb5658..6c2c97a980 100644
> > --- a/fs/ocfs2/ocfs2_trace.h
> > +++ b/fs/ocfs2/ocfs2_trace.h
> > @@ -1246,22 +1246,20 @@ TRACE_EVENT(ocfs2_write_end_inline,
> >
> >  TRACE_EVENT(ocfs2_fault,
> >       TP_PROTO(unsigned long long ino,
> > -              void *area, void *page, unsigned long pgoff),
> > -     TP_ARGS(ino, area, page, pgoff),
> > +              void *page, unsigned long pgoff),
> > +     TP_ARGS(ino, page, pgoff),
> >       TP_STRUCT__entry(
> >               __field(unsigned long long, ino)
> > -             __field(void *, area)
> >               __field(void *, page)
> >               __field(unsigned long, pgoff)
> >       ),
> >       TP_fast_assign(
> >               __entry->ino = ino;
> > -             __entry->area = area;
> >               __entry->page = page;
> >               __entry->pgoff = pgoff;
> >       ),
> > -     TP_printk("%llu %p %p %lu",
> > -               __entry->ino, __entry->area, __entry->page, __entry->pgoff)
> > +     TP_printk("%llu %p %lu",
> > +               __entry->ino, __entry->page, __entry->pgoff)
> >  );
> >
> >  /* End of trace events for fs/ocfs2/mmap.c. */
>