[PATCH] knfsd: nfsd: call nfsd_setuser() on fh_compose(), fix nfsd4 permissions problem

In the typical v2/v3 case the only new filehandles used as arguments to
operations are filehandles taken directly off the wire, which don't get
dentries until fh_verify() is called.

But in v4 the filehandles that are arguments to operations were often created
by previous operations (putrootfh, lookup, etc.) using fh_compose, which sets
the dentry in the filehandle without calling nfsd_setuser().

This also means that, for example, if filesystem B is mounted on filesystem A,
and filesystem A is exported without root-squashing, then a client can bypass
the rootsquashing on B using a compound that starts at a filehandle in A,
crosses into B using lookups, and then does stuff in B.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 8 insertions, 7 deletions

diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
index ca96ede30a10..ecc439d2565f 100644
--- a/fs/nfsd/nfsfh.c
+++ b/fs/nfsd/nfsfh.c
@@ -187,13 +187,6 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, int type, int access)
                         goto out;
                 }
 
-                /* Set user creds for this exportpoint */
-                error = nfsd_setuser(rqstp, exp);
-                if (error) {
-                        error = nfserrno(error);
-                        goto out;
-                }
-
                 /*
                  * Look up the dentry using the NFS file handle.
                  */
@@ -251,6 +244,14 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, int type, int access)
         }
         cache_get(&exp->h);
 
+        /* Set user creds for this exportpoint; necessary even in the "just
+         * checking" case because this may be a filehandle that was created by
+         * fh_compose, and that is about to be used in another nfsv4 compound
+         * operation */
+        error = nfserrno(nfsd_setuser(rqstp, exp));
+        if (error)
+                goto out;
+
         error = nfsd_mode_check(rqstp, dentry->d_inode->i_mode, type);
         if (error)
                 goto out;