[Gluster-devel] Fixing setfsuid/gid problems in posix xlator

Pranith Kumar Karampuri pkarampu at redhat.com
Fri Sep 23 15:14:14 UTC 2016

On Fri, Sep 23, 2016 at 6:12 PM, Jeff Darcy <jdarcy at redhat.com> wrote:

> > Jiffin found an interesting problem in posix xlator where we have never
> been
> > using setfsuid/gid ( http://review.gluster.org/#/c/15545/ ), what I am
> > seeing regressions after this is, if the files are created using non-root
> > user then the file creation fails because that user doesn't have
> permissions
> > to create the gfid-link. So it seems like the correct way forward for
> this
> > patch is to write wrappers around sys_<syscall> to do setfsuid/gid do the
> > actual operation requested and then set it back to old uid/gid and then
> do
> > the internal operations. I am planning to write posix_sys_<syscall>() to
> do
> > the same, may be a macro?
> Kind of an aside, but I'd prefer to see a lot fewer macros in our code.
> They're not type-safe, and multi-line macros often mess up line numbers for
> debugging or error messages.  IMO it's better to use functions whenever
> possible, and usually to let the compiler worry about how/when to inline.
> > I need inputs from you guys to let me know if I am on the right path and
> if
> > you see any issues with this approach.
> I think there's a bit of an interface problem here.  The sys_xxx wrappers
> don't have arguments that point to the current frame, so how would they get
> the correct uid/gid?  We could add arguments to each function, but then
> we'd have to modify every call.  This includes internal calls which don't
> have a frame to pass, so I guess they'd have to pass NULL.  Alternatively,
> we could create a parallel set of functions with frame pointers.  Contrary
> to what I just said above, this might be a case where macros make sense:
>    int
>    sys_writev_fp (call_frame_t *frame, int fd, void *buf, size_t len)
>    {
>       if (frame) { setfsuid(...) ... }
>       int ret = writev (fd, buf, len);
>       if (frame) { setfsuid(...) ... }
>       return ret;
>    }
>    #define sys_writev(fd,buf,len) sys_writev_fp (NULL, fd, buf, len)
> That way existing callers don't have to change, but posix can use the
> extended versions to get the right setfsuid behavior.
After trying to do these modifications to test things out, I am now under
the impression to remove setfsuid/gid altogether and depend on posix-acl
for permission checks. It seems too cumbersome as the operations more often
than not happen on files inside .glusterfs and non-root users/groups don't
have permissions at all to access files in that directory.

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