Re: [PATCH 5.15] ovl: fix null pointer dereference in ovl_get_acl_rcu()

[Zhihao Cheng]

在 2023/7/17 2:26, Amir Goldstein 写道:
> On Mon, Jul 10, 2023 at 6:29 AM Zhihao Cheng <chengzhihao1@xxxxxxxxxx> wrote:
> > [ Upstream commit f4e19e595cc2e76a8a58413eb19d3d9c51328b53 ]
> >
> > Following process:
> >           P1                     P2
> >   path_openat
> >    link_path_walk
> >     may_lookup
> >      inode_permission(rcu)
> >       ovl_permission
> >        acl_permission_check
> >         check_acl
> >          get_cached_acl_rcu
> >           ovl_get_inode_acl
> >            realinode = ovl_inode_real(ovl_inode)
> >                                drop_cache
> >                                 __dentry_kill(ovl_dentry)
> >                                  iput(ovl_inode)
> >                                   ovl_destroy_inode(ovl_inode)
> >                                    dput(oi->__upperdentry)
> >                                     dentry_kill(upperdentry)
> >                                      dentry_unlink_inode
> >                                       upperdentry->d_inode = NULL
> >              ovl_inode_upper
> >               upperdentry = ovl_i_dentry_upper(ovl_inode)
> >               d_inode(upperdentry) // returns NULL
> >            IS_POSIXACL(realinode) // NULL pointer dereference
> > , will trigger an null pointer dereference at realinode:
> >    [  205.472797] BUG: kernel NULL pointer dereference, address:
> >                   0000000000000028
> >    [  205.476701] CPU: 2 PID: 2713 Comm: ls Not tainted
> >                   6.3.0-12064-g2edfa098e750-dirty #1216
> >    [  205.478754] RIP: 0010:do_ovl_get_acl+0x5d/0x300
> >    [  205.489584] Call Trace:
> >    [  205.489812]  <TASK>
> >    [  205.490014]  ovl_get_inode_acl+0x26/0x30
> >    [  205.490466]  get_cached_acl_rcu+0x61/0xa0
> >    [  205.490908]  generic_permission+0x1bf/0x4e0
> >    [  205.491447]  ovl_permission+0x79/0x1b0
> >    [  205.491917]  inode_permission+0x15e/0x2c0
> >    [  205.492425]  link_path_walk+0x115/0x550
> >    [  205.493311]  path_lookupat.isra.0+0xb2/0x200
> >    [  205.493803]  filename_lookup+0xda/0x240
> >    [  205.495747]  vfs_fstatat+0x7b/0xb0
> >
> > Fetch a reproducer in [Link].
> >
> > Use the helper ovl_i_path_realinode() to get realinode and then do
> > non-nullptr checking.
> >
> > There are some changes from upstream commit:
> > 1. Corrusponds to do_ovl_get_acl() in 5.15 is ovl_get_acl()
> > 2. ovl_i_path_real is not imported in 5.15, we can get realinode by
> >     ovl_inode_real
> > 3. CONFIG_FS_POSIX_ACL checking is dropped in commit
> >     ded536561a3674327dfa4bb389085705cae22b8a ("ovl: improve ovl_get_acl()
> >     if POSIX ACL support is off"), we still keep it in 5.15.
>
> Zhihao,
>
> Can you please provide also the backport for 6.1.

Sure, I sent it out, please refer to 
https://lore.kernel.org/stable/20230717030904.1669754-1-chengzhihao1@xxxxxxxxxx/T/#t.

> Basically, the same as this one without the CONFIG_FS_POSIX_ACL check.
>
> Thanks,
> Amir.
>
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=217404
> > Fixes: 332f606b32b6 ("ovl: enable RCU'd ->get_acl()")
> > Cc: <stable@xxxxxxxxxxxxxxx> # v5.15
> > Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
> > Suggested-by: Christian Brauner <brauner@xxxxxxxxxx>
> > Suggested-by: Amir Goldstein <amir73il@xxxxxxxxx>
> > Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> > Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> > ---
> >   fs/overlayfs/inode.c | 10 +++++++++-
> >   1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> > index d41f0c8e0e2a..65e5e6eb761a 100644
> > --- a/fs/overlayfs/inode.c
> > +++ b/fs/overlayfs/inode.c
> > @@ -453,7 +453,15 @@ struct posix_acl *ovl_get_acl(struct inode *inode, int type, bool rcu)
> >          const struct cred *old_cred;
> >          struct posix_acl *acl;
> >
> > -       if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode))
> > +       if (!IS_ENABLED(CONFIG_FS_POSIX_ACL))
> > +               return NULL;
> > +
> > +       if (!realinode) {
> > +               WARN_ON(!rcu);
> > +               return ERR_PTR(-ECHILD);
> > +       }
> > +
> > +       if (!IS_POSIXACL(realinode))
> >                  return NULL;
> >
> >          if (rcu)
> > --
> > 2.39.2
> .