Re: [PATCH v13 10/28] ovl: Modify ovl_lookup() and friends to lookup metacopy dentry

[Vivek Goyal <vgoyal@redhat.com>]

On Fri, Mar 30, 2018 at 08:49:26AM +0300, Amir Goldstein wrote:
> On Thu, Mar 29, 2018 at 10:38 PM, Vivek Goyal <vgoyal@redhat.com> wrote:
> > This patch modifies ovl_lookup() and friends to lookup metacopy dentries.
> > It also allows for presence of metacopy dentries in lower layer.
> >
> > During lookup, check for presence of OVL_XATTR_METACOPY and if not present,
> > set OVL_UPPERDATA bit in flags.
> >
> > We don't support metacopy feature with nfs_export. So in nfs_export code,
> > we set OVL_UPPERDATA flag set unconditionally if upper inode exists.
> >
> > Do not follow metacopy origin if we find a metacopy only inode and metacopy
> > feature is not enabled for that mount. Like redirect, this can have security
> > implications where an attacker could hand craft upper and try to gain
> > access to file on lower which it should not have to begin with.
> >
> > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> > ---
> >  fs/overlayfs/export.c    |  3 ++
> >  fs/overlayfs/inode.c     |  6 +++-
> >  fs/overlayfs/namei.c     | 90 ++++++++++++++++++++++++++++++++++++++++++------
> >  fs/overlayfs/overlayfs.h |  1 +
> >  fs/overlayfs/util.c      | 22 ++++++++++++
> >  5 files changed, 110 insertions(+), 12 deletions(-)
> >
> > diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
> > index e668329f7361..1c233096e59c 100644
> > --- a/fs/overlayfs/export.c
> > +++ b/fs/overlayfs/export.c
> > @@ -311,6 +311,9 @@ static struct dentry *ovl_obtain_alias(struct super_block *sb,
> >                 return ERR_CAST(inode);
> >         }
> >
> > +       if (upper)
> > +               ovl_set_flag(OVL_UPPERDATA, inode);
> > +
> >         dentry = d_find_any_alias(inode);
> >         if (!dentry) {
> >                 dentry = d_alloc_anon(inode->i_sb);
> > diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> > index 3991a890b464..e1dbfed0c449 100644
> > --- a/fs/overlayfs/inode.c
> > +++ b/fs/overlayfs/inode.c
> > @@ -677,7 +677,7 @@ struct inode *ovl_get_inode(struct super_block *sb, struct dentry *upperdentry,
> >         struct inode *realinode = upperdentry ? d_inode(upperdentry) : NULL;
> >         struct inode *inode;
> >         bool bylower = ovl_hash_bylower(sb, upperdentry, lowerdentry, index);
> > -       bool is_dir;
> > +       bool is_dir, metacopy = false;
> >
> >         if (!realinode)
> >                 realinode = d_inode(lowerdentry);
> > @@ -732,6 +732,10 @@ struct inode *ovl_get_inode(struct super_block *sb, struct dentry *upperdentry,
> >         if (index)
> >                 ovl_set_flag(OVL_INDEX, inode);
> >
> > +       metacopy = ovl_check_metacopy_xattr(upperdentry ?: lowerdentry);
> 
> No reason to check metacopy on lowerdentry.

Right. Will change it.

> 
> > +       if (upperdentry && !metacopy)
> > +               ovl_set_flag(OVL_UPPERDATA, inode);
> > +
> >         OVL_I(inode)->redirect = redirect;
> >
> >         /* Check for non-merge dir that may have whiteouts */
> > diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> > index 0b325e65864c..1dba89e9543f 100644
> > --- a/fs/overlayfs/namei.c
> > +++ b/fs/overlayfs/namei.c
> > @@ -24,6 +24,7 @@ struct ovl_lookup_data {
> >         bool stop;
> >         bool last;
> >         char *redirect;
> > +       bool metacopy;
> >  };
> >
> >  static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
> > @@ -252,9 +253,13 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
> >                 goto put_and_out;
> >         }
> >         if (!d_can_lookup(this)) {
> > -               d->stop = true;
> 
> upper was a dir. You look in lower and find a non-dir. you need to stop
> going to next layer. goto put_and_out won't do that.

Ok, will set d->stop = true before "goto put_and_out" to handle this
case.

> 
> Similarly, you need to handle the case where dir is found below
> non-dir with metacopy.

Ok, will look into it.

> 
> >                 if (d->is_dir)
> >                         goto put_and_out;
> > +               err = ovl_check_metacopy_xattr(this);
> > +               if (err < 0)
> > +                       goto out_err;
> > +               d->stop = !err;
> > +               d->metacopy = !!err;
> >                 goto out;
> >         }
> >         if (last_element)
> > @@ -815,7 +820,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >         struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
> >         struct ovl_entry *poe = dentry->d_parent->d_fsdata;
> >         struct ovl_entry *roe = dentry->d_sb->s_root->d_fsdata;
> > -       struct ovl_path *stack = NULL;
> > +       struct ovl_path *stack = NULL, *origin_path = NULL;
> >         struct dentry *upperdir, *upperdentry = NULL;
> >         struct dentry *origin = NULL;
> >         struct dentry *index = NULL;
> > @@ -826,6 +831,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >         struct dentry *this;
> >         unsigned int i;
> >         int err;
> > +       bool metacopy = false;
> >         struct ovl_lookup_data d = {
> >                 .name = dentry->d_name,
> >                 .is_dir = false,
> > @@ -833,6 +839,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >                 .stop = false,
> >                 .last = ofs->config.redirect_follow ? false : !poe->numlower,
> >                 .redirect = NULL,
> > +               .metacopy = false,
> >         };
> >
> >         if (dentry->d_name.len > ofs->namelen)
> > @@ -851,7 +858,8 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >                         goto out;
> >                 }
> >                 if (upperdentry && !d.is_dir) {
> > -                       BUG_ON(!d.stop || d.redirect);
> > +                       unsigned int origin_ctr = 0;
> > +                       BUG_ON(d.redirect);
> >                         /*
> >                          * Lookup copy up origin by decoding origin file handle.
> >                          * We may get a disconnected dentry, which is fine,
> > @@ -862,16 +870,20 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >                          * number - it's the same as if we held a reference
> >                          * to a dentry in lower layer that was moved under us.
> >                          */
> > -                       err = ovl_check_origin(ofs, upperdentry, &stack, &ctr);
> > +                       err = ovl_check_origin(ofs, upperdentry, &origin_path,
> > +                                              &origin_ctr);
> >                         if (err)
> >                                 goto out_put_upper;
> > +
> > +                       if (d.metacopy)
> > +                               metacopy = true;
> >                 }
> >
> >                 if (d.redirect) {
> >                         err = -ENOMEM;
> >                         upperredirect = kstrdup(d.redirect, GFP_KERNEL);
> >                         if (!upperredirect)
> > -                               goto out_put_upper;
> > +                               goto out_put_origin;
> >                         if (d.redirect[0] == '/')
> >                                 poe = roe;
> >                 }
> > @@ -883,7 +895,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >                 stack = kcalloc(ofs->numlower, sizeof(struct ovl_path),
> >                                 GFP_KERNEL);
> >                 if (!stack)
> > -                       goto out_put_upper;
> > +                       goto out_put_origin;
> >         }
> >
> >         for (i = 0; !d.stop && i < poe->numlower; i++) {
> > @@ -905,7 +917,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >                  * If no origin fh is stored in upper of a merge dir, store fh
> >                  * of lower dir and set upper parent "impure".
> >                  */
> > -               if (upperdentry && !ctr && !ofs->noxattr) {
> > +               if (upperdentry && !ctr && !ofs->noxattr && d.is_dir) {
> >                         err = ovl_fix_origin(dentry, this, upperdentry);
> >                         if (err) {
> >                                 dput(this);
> > @@ -917,16 +929,35 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >                  * When "verify_lower" feature is enabled, do not merge with a
> >                  * lower dir that does not match a stored origin xattr. In any
> >                  * case, only verified origin is used for index lookup.
> > +                *
> > +                * For non-dir dentry, make sure dentry found by lookup
> > +                * matches the origin stored in upper. Otherwise its an
> > +                * error.
> >                  */
> > -               if (upperdentry && !ctr && ovl_verify_lower(dentry->d_sb)) {
> > +               if (upperdentry && !ctr &&
> > +                   ((d.is_dir && ovl_verify_lower(dentry->d_sb)) ||
> > +                    (!d.is_dir && origin_path))) {
> >                         err = ovl_verify_origin(upperdentry, this, false);
> >                         if (err) {
> >                                 dput(this);
> > -                               break;
> > +                               if (d.is_dir)
> > +                                       break;
> > +                               goto out_put;
> >                         }
> > -
> >                         /* Bless lower dir as verified origin */
> > -                       origin = this;
> > +                       if (d.is_dir)
> > +                               origin = this;
> 
> It's ok to bless verified non-dir as well.
> It is going to be blesses anyway, just above index lookup if ctr > 0.

Hmm..., make sense to trust origin once we have verified origin both
for dir and non-dir. Will do.

> 
> > +               }
> > +
> > +               if (d.metacopy)
> > +                       metacopy = true;
> > +               /*
> > +                * Do not store intermediate metacopy dentries in chain,
> > +                * except top most lower metacopy dentry
> > +                */
> > +               if (d.metacopy && ctr) {
> > +                       dput(this);
> > +                       continue;
> >                 }
> >
> >                 stack[ctr].dentry = this;
> > @@ -960,6 +991,34 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >                 }
> >         }
> >
> > +       if (metacopy) {
> > +               BUG_ON(d.is_dir);
> 
> Yeh, I think that is really a bug, because you need to detect
> the case of dir in lower layer under metacopy in upper layer
> and do something about it.
> 
> > +               /*
> > +                * Found a metacopy dentry but did not find corresponding
> > +                * data dentry
> > +                */
> > +               if (d.metacopy) {
> > +                       err = -ESTALE;
> > +                       goto out_put;
> > +               }
> > +
> > +               err = -EPERM;
> > +               if (!ofs->config.metacopy) {
> > +                       pr_warn_ratelimited("overlay: refusing to follow"
> > +                                           " metacopy origin for (%pd2)\n",
> > +                                           dentry);
> > +                       goto out_put;
> > +               }
> > +       } else if (!d.is_dir && upperdentry && !ctr && origin_path) {
> > +               if (WARN_ON(stack != NULL)) {
> > +                       err = -EIO;
> > +                       goto out_put;
> > +               }
> > +               stack = origin_path;
> > +               ctr = 1;
> > +               origin_path = NULL;
> > +       }
> > +
> >         /*
> >          * Lookup index by lower inode and verify it matches upper inode.
> >          * We only trust dir index if we verified that lower dir matches
> > @@ -1006,6 +1065,10 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >         }
> >
> >         revert_creds(old_cred);
> > +       if (origin_path) {
> > +               dput(origin_path->dentry);
> > +               kfree(origin_path);
> > +       }
> >         dput(index);
> >         kfree(stack);
> >         kfree(d.redirect);
> > @@ -1019,6 +1082,11 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> >         for (i = 0; i < ctr; i++)
> >                 dput(stack[i].dentry);
> >         kfree(stack);
> > +out_put_origin:
> > +       if (origin_path) {
> > +               dput(origin_path->dentry);
> > +               kfree(origin_path);
> > +       }
> 
> There is no need for the new goto label.
> Just add this in existing out_put_upper label.

Ok, I should be able to club this with out_put_upper label.

Vivek

> 
> Thanks,
> Amir,