Date: Tue, 16 Oct 2001 16:32:27 -0400 (EDT) From: Robert Watson <rwatson@freebsd.org> To: Bruce Evans <bde@zeta.org.au> Cc: current@freebsd.org, stable@freebsd.org, dillon@freebsd.org, alfred@freebsd.org Subject: Re: coredump() broken for nfs filesystems Message-ID: <Pine.NEB.3.96L.1011016163117.12283G-100000@fledge.watson.org> In-Reply-To: <20011015211333.B576-100000@delplex.bde.org>
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As I've mentioned before, the current credential-munging here is simply
broken; however, the brokenness I previously observed is independent of
the brokenness you are now reporting.
Robert N M Watson FreeBSD Core Team, TrustedBSD Project
robert@fledge.watson.org NAI Labs, Safeport Network Services
On Mon, 15 Oct 2001, Bruce Evans wrote:
> coredump() now usually creates empty core files for nfs filesystems.
> This seems to be caused by the changes in rev.1.132 (-current) and
> rev.1.72.2.9 (RELENG_4), and braindamage in nfs_dolock():
>
> Index: kern_sig.c
> ===================================================================
> RCS file: /home/ncvs/src/sys/kern/kern_sig.c,v
> retrieving revision 1.131
> retrieving revision 1.132
> diff -u -2 -r1.131 -r1.132
> --- kern_sig.c 6 Sep 2001 22:20:41 -0000 1.131
> +++ kern_sig.c 8 Sep 2001 20:02:32 -0000 1.132
> > ...
> @@ -1896,6 +1898,17 @@
> NDFREE(&nd, NDF_ONLY_PNBUF);
> vp = nd.ni_vp;
> +
> + VOP_UNLOCK(vp, 0, p);
> + lf.l_whence = SEEK_SET;
> + lf.l_start = 0;
> + lf.l_len = 0;
> + lf.l_type = F_WRLCK;
> + error = VOP_ADVLOCK(vp, (caddr_t)p, F_SETLK, &lf, F_FLOCK);
> + if (error)
> + goto out2;
> +
>
> This usually goes to out2 with error EOPNOTSUPP if the core file is on
> an nfs filesystem.
>
> From nfs_dolock():
>
> % /*
> % * XXX Hack to temporarily allow this process (regardless of it's creds)
> % * to open the fifo we need to write to. vn_open() really should
> % * take a ucred (and once it does, this code should be fixed to use
> % * proc0's ucred.
> % */
> % saved_uid = p->p_ucred->cr_uid;
> % p->p_ucred->cr_uid = 0; /* temporarly run the vn_open as root */
> %
> % fmode = FFLAGS(O_WRONLY);
> % error = vn_open(&nd, &fmode, 0);
>
> This vn_open() usually fails, because root is usually mapped so has even
> less write permission than most users. I don't see how nfs write locks can
> work for syscalls either.
>
> % p->p_ucred->cr_uid = saved_uid;
> % if (error != 0) {
> % return (error == ENOENT ? EOPNOTSUPP : error);
> % }
>
> EOPNOTSUPP is a strange error for foot shooting.
>
> Bruce
>
>
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