Fix a condition where nfs_statfs() can precipitate a panic. There is

code that says this:

        nfsm_request(vp, NFSPROC_FSSTAT, p, cred);
        if (v3)
                nfsm_postop_attr(vp, retattr);
        if (!error)
                nfsm_dissect(sfp, struct nfs_statfs *, NFSX_STATFS(v3));

The problem here is that if error != 0, nfsm_dissect() will not be
called, which leaves sfp == NULL. But nfs_statfs() does not bail out
at this point: it continues processing until it tries to dereference
sfp, which causes a panic. I was able to generate this crash under
the following conditions:

1) Set up a machine as an NFS server and NFS client, with amd running
   (using NIS maps). /usr/local is exported, though any exported fs
   can can be used to trigger the bug.
2) Log in as normal user, with home directory mounted from a SunOS 4.1.3
   NFS server via amd (along with a few other NFS filesystems from same
   machine).
3) Su to root and type the following:
   # mount localhost:/usr/local /mnt
   # df

To fix the panic, I changed the code to read:

        if (!error) {
                nfsm_dissect(sfp, struct nfs_statfs *, NFSX_STATFS(v3));
        } else
                goto nfsmout;

This is a bit kludgy in that nfsmout is a label defined by the nfsm_subs.h
macros, but these macros are themselves more than a little kludgy. This
stops the machine from crashing, but does not fix the overall bug: 'error'
somehow becomes 5 (EIO) when a statfs() is performed on the locally mounted
NFS filesystem. This seems to only happen the first time the filesystem
is accesed: on subsequent accesses, it seems to work fine again.

Now, I know there's no practical use in mounting a local filesystem
via NFS, but doing it shouldn't cause the system to melt down.

1 files changed, 5 insertions, 2 deletions

diff --git a/sys/nfsclient/nfs_vfsops.c b/sys/nfsclient/nfs_vfsops.c
index 9bcc0f7..f867948 100644
--- a/sys/nfsclient/nfs_vfsops.c
+++ b/sys/nfsclient/nfs_vfsops.c
@@ -34,7 +34,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)nfs_vfsops.c	8.12 (Berkeley) 5/20/95
- * $Id: nfs_vfsops.c,v 1.42 1997/05/12 19:02:56 tegge Exp $
+ * $Id: nfs_vfsops.c,v 1.43 1997/06/03 17:22:47 dfr Exp $
  */
 
 #include <sys/param.h>
@@ -269,8 +269,11 @@ nfs_statfs(mp, sbp, p)
 	nfsm_request(vp, NFSPROC_FSSTAT, p, cred);
 	if (v3)
 		nfsm_postop_attr(vp, retattr);
-	if (!error)
+	if (!error) {
 		nfsm_dissect(sfp, struct nfs_statfs *, NFSX_STATFS(v3));
+	} else
+		goto nfsmout;
+
 #ifdef __NetBSD__
 #ifdef COMPAT_09
 	sbp->f_type = 2;