Re: [PATCH AUTOSEL 4.14 090/108] ovl: verify permissions in ovl_path_open()

Naresh Kamboju
2020-06-23T18:28:46Z

On Tue, 23 Jun 2020 at 22:46, Sasha Levin <sashal@kernel.org> wrote:
>
> On Tue, Jun 23, 2020 at 08:55:38PM +0530, Naresh Kamboju wrote:
> >On Thu, 18 Jun 2020 at 07:18, Sasha Levin <sashal@kernel.org> wrote:
> >>
> >> From: Miklos Szeredi <mszeredi@redhat.com>
> >>
> >> [ Upstream commit 56230d956739b9cb1cbde439d76227d77979a04d ]
> >>
> >> Check permission before opening a real file.
> >>
> >> ovl_path_open() is used by readdir and copy-up routines.
> >>
> >> ovl_permission() theoretically already checked copy up permissions, but it
> >> doesn't hurt to re-do these checks during the actual copy-up.
> >>
> >> For directory reading ovl_permission() only checks access to topmost
> >> underlying layer. Readdir on a merged directory accesses layers below the
> >> topmost one as well. Permission wasn't checked for these layers.
> >>
> >> Note: modifying ovl_permission() to perform this check would be far more
> >> complex and hence more bug prone. The result is less precise permissions
> >> returned in access(2). If this turns out to be an issue, we can revisit
> >> this bug.
> >>
> >> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
> >> Signed-off-by: Sasha Levin <sashal@kernel.org>
> >> ---
> >> fs/overlayfs/util.c | 27 ++++++++++++++++++++++++++-
> >> 1 file changed, 26 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> >> index afdc2533ce74..76d6610767f6 100644
> >> --- a/fs/overlayfs/util.c
> >> +++ b/fs/overlayfs/util.c
> >> @@ -307,7 +307,32 @@ bool ovl_is_whiteout(struct dentry *dentry)
> >>
> >> struct file *ovl_path_open(struct path *path, int flags)
> >> {
> >> - return dentry_open(path, flags | O_NOATIME, current_cred());
> >> + struct inode *inode = d_inode(path->dentry);
> >> + int err, acc_mode;
> >> +
> >> + if (flags & ~(O_ACCMODE | O_LARGEFILE))
> >> + BUG();
> >> +
> >> + switch (flags & O_ACCMODE) {
> >> + case O_RDONLY:
> >> + acc_mode = MAY_READ;
> >> + break;
> >> + case O_WRONLY:
> >> + acc_mode = MAY_WRITE;
> >> + break;
> >> + default:
> >> + BUG();
> >
> >This BUG: triggered on stable-rc 5.7, 5.4, 4.19 and 4.14.
> >
> >steps to reproduce:
> > - cd /opt/ltp
> > - ./runltp -s execveat03
>
> Yup, that patch has been dropped, thanks for testing!

After reverting this patch I see these messages while testing LTP execveat03.
[ 87.931537] overlayfs: upper fs does not support RENAME_WHITEOUT.
[ 87.937693] overlayfs: upper fs does not support xattr, falling back
to index=off and metacopy=off.>

- Naresh

> --
> Thanks,
> Sasha