Re: [linux-next:master] [fs] 1b43c46297: kernel_BUG_at_mm/usercopy.c

[Jan Kara]

On Wed 03-04-24 10:46:19, Christian Brauner wrote:
> On Wed, Apr 03, 2024 at 02:54:14PM +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)) {
> 
> Groan, of course. What a silly mistake. Thanks for the fix.
> I'll fold this into:
> Fixes: 1b43c4629756 ("fs: Annotate struct file_handle with __counted_by() and use struct_size()")
> because this hasn't hit mainline yet and it doesn't make sense to keep
> that bug around.
> 
> Sorry, that'll mean we drop your patch but I'll give you credit in the
> commit log of the original patch.

Indeed, I should have caught this during review. Sorry for that and thanks
for fixing this up quickly.

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR