Re: linux-next: Tree for Jan 20 -- Kernel panic - Unable to mount root fs

Paul Moore
2015-01-21T00:14:54Z

On Tuesday, January 20, 2015 07:04:54 PM Paul Moore wrote:
> On Wednesday, January 21, 2015 12:27:26 AM Sabrina Dubroca wrote:
> > 2015-01-20, 23:17:25 +0000, Al Viro wrote:
> > > On Tue, Jan 20, 2015 at 10:50:41PM +0000, Al Viro wrote:
> > > > doesn't look at _anything_ other than name->name other than for
> > > > audit_inode(). And name->name is apparently the same.
> > > >
> > > > It looks like something ends up buggering name->name in process, but
> > > > then
> > > > the damn thing appears to be normal after return from
> > > > filename_lookup()...
> > >
> > > If my reconstruction of what's going on is correct, the call chain here
> > > is do_path_lookup() <- kern_path() <- lookup_bdev() <-
> > > blkdev_get_by_path()
> > > <- mount_bdev() <- some_type.mount() <- mount_fs()
> > > <- vfs_kern_mount() <- do_new_mount() <- do_mount() <- sys_mount()
> > > <- do_mount_root() <- mount_block_root() <- mount_root(). Which is
> > > obscenely long, BTW, but that's a separate story...
> > >
> > > Could you slap
> > >
> > > struct stat buf;
> > > int n = sys_newstat(name, &buf);
> > > printk(KERN_ERR "stat(\"%s\") -> %d\n", name, n);
> > > n = sys_newstat("/dev", &buf);
> > > printk(KERN_ERR "stat(\"dev\") -> %d\n", n);
> > >
> > > in the beginning of mount_block_root() (init/do_mounts.c) and see what
> > > it
> > > prints?
> >
> > I get
> >
> > stat("/dev/root") -> -2
> > stat("dev") -> -2
> > with the patch applied (+panic)
> >
> >
> > and:
> >
> > stat("/dev/root") -> 0
> > stat("dev") -> 0
> > with the old version of do_path_lookup.
>
> Wait a minute ... at this early stage of boot, I'm pretty sure we don't have
> a valid current->audit_context since we haven't fork'd anything. If the
> audit context was non-NULL garbage that might explain the panic ...

Could you try initializing the init_task's audit_context to NULL in the
INIT_TASK macro in include/linux/init_task.h?

Example:

#define INIT_TASK(tsk)
{
.state = 0,
.stack = &init_thread_info,
...
.audit_context = NULL,
...
}

--
paul moore
security @ redhat