Re: [PATCH next] fs: fix oob in do_handle_open

[Christian Brauner]

On Wed, Apr 03, 2024 at 04:48:17AM -0400, Jeff Layton wrote:
> On Wed, 2024-04-03 at 14:54 +0800, Edward Adam Davis wrote:
> > [Syzbot reported]
> > BUG: KASAN: slab-out-of-bounds in instrument_copy_from_user_before include/linux/instrumented.h:129 [inline]
> > BUG: KASAN: slab-out-of-bounds in _copy_from_user+0x7b/0xe0 lib/usercopy.c:22
> > Write of size 48 at addr ffff88802b8cbc88 by task syz-executor333/5090
> > 
> > CPU: 0 PID: 5090 Comm: syz-executor333 Not tainted 6.9.0-rc2-next-20240402-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
> > Call Trace:
> >  <TASK>
> >  __dump_stack lib/dump_stack.c:88 [inline]
> >  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
> >  print_address_description mm/kasan/report.c:377 [inline]
> >  print_report+0x169/0x550 mm/kasan/report.c:488
> >  kasan_report+0x143/0x180 mm/kasan/report.c:601
> >  kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
> >  instrument_copy_from_user_before include/linux/instrumented.h:129 [inline]
> >  _copy_from_user+0x7b/0xe0 lib/usercopy.c:22
> >  copy_from_user include/linux/uaccess.h:183 [inline]
> >  handle_to_path fs/fhandle.c:203 [inline]
> >  do_handle_open+0x204/0x660 fs/fhandle.c:226
> >  do_syscall_64+0xfb/0x240
> >  entry_SYSCALL_64_after_hwframe+0x72/0x7a
> > [Fix] 
> > When copying data to f_handle, the length of the copied data should not include
> > the length of "struct file_handle".
> > 
> > Reported-by: syzbot+4139435cb1b34cf759c2@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
> > ---
> >  fs/fhandle.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/fs/fhandle.c b/fs/fhandle.c
> > index 53ed54711cd2..8a7f86c2139a 100644
> > --- a/fs/fhandle.c
> > +++ b/fs/fhandle.c
> > @@ -202,7 +202,7 @@ static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
> >  	*handle = f_handle;
> >  	if (copy_from_user(&handle->f_handle,
> >  			   &ufh->f_handle,
> > -			   struct_size(ufh, f_handle, f_handle.handle_bytes))) {
> > +			   f_handle.handle_bytes)) {
> >  		retval = -EFAULT;
> >  		goto out_handle;
> >  	}
> 
> cc'ing Gustavo, since it looks like his patch in -next is what broke
> this.

I'ved folded the fix into Gustavo's patch. Please see
https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git/commit/?h=vfs.misc&id=02426828cde24cd5b6cf5f30467cea085118f657