On Fri, 2020-01-31 at 12:20 +0000, Al Viro wrote:
> On Fri, Jan 31, 2020 at 10:08:37AM +0000, Rantala, Tommi T. (Nokia -
> FI/Espoo) wrote:
> > On Tue, 2020-01-28 at 15:08 +0100, Greg Kroah-Hartman wrote:
> > > From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> > >
> > > @@ -3258,6 +3259,8 @@ static int do_last(struct nameidata *nd,
> > > struct file *file, const struct open_flags *op)
> > > {
> > > struct dentry *dir = nd->path.dentry;
> > > + kuid_t dir_uid = dir->d_inode->i_uid;
> >
> > I hit the following oops in 4.19.100 while running kselftests.
> >
> > fs/namei.c:3262 matches the line above.
> >
> > Any ideas?
>
> Yes. Make those two line
> kuid_t dir_uid = nd->inode->i_uid;
> umode_t dir_mode = nd->inode->i_mode;
>
> I'm pretty sure that I know which way I'd fucked up there; we can
> get here in RCU mode with stale nd->path.dentry (that would make
> the thing fail with -ECHILD. with retry in non-RCU mode). In
> non-stale case nd->inode is the same as nd->path.dentry->d_inode
> and it's always pointing to a struct inode that hadn't been
> freed yet.
The oops does not seem to reproduce easily with kselftests, I've only hit
it once with 4.19.100.
Made the change in fs/namei.c, so far no ill effects.
I'll continue running the kselftests...
-Tommi
