nfsd: simplify fh_verify access checks

All nfsd security depends on the security checks in fh_verify, and
especially on nfsd_setuser().

It therefore bothers me that the nfsd_setuser call may be made from
three different places, depending on whether the filehandle has already
been mapped to a dentry, and on whether subtreechecking is in force.

Instead, make an unconditional call in fh_verify(), so it's trivial to
verify that the call always occurs.

That leaves us with a redundant nfsd_setuser() call in the subtreecheck
case--it needs the correct user set earlier in order to check execute
permissions on the path to this filehandle--but I'm willing to accept
that minor inefficiency in the subtreecheck case in return for more
straightforward permission checking.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
index d0d8a21..a77efb8 100644 (file)
--- a/fs/nfsd/nfsfh.c
+++ b/fs/nfsd/nfsfh.c
@@ -233,14 +233,6 @@ static __be32 nfsd_set_fh_dentry(struct svc_rqst *rqstp, struct svc_fh *fhp)
                goto out;
        }
 
-       if (exp->ex_flags & NFSEXP_NOSUBTREECHECK) {
-               error = nfsd_setuser_and_check_port(rqstp, exp);
-               if (error) {
-                       dput(dentry);
-                       goto out;
-               }
-       }
-
        if (S_ISDIR(dentry->d_inode->i_mode) &&
                        (dentry->d_flags & DCACHE_DISCONNECTED)) {
                printk("nfsd: find_fh_dentry returned a DISCONNECTED directory: %s/%s\n",
@@ -295,28 +287,28 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, int type, int access)
                error = nfsd_set_fh_dentry(rqstp, fhp);
                if (error)
                        goto out;
-               dentry = fhp->fh_dentry;
-               exp = fhp->fh_export;
-       } else {
-               /*
-                * just rechecking permissions
-                * (e.g. nfsproc_create calls fh_verify, then nfsd_create
-                * does as well)
-                */
-               dprintk("nfsd: fh_verify - just checking\n");
-               dentry = fhp->fh_dentry;
-               exp = fhp->fh_export;
-               /*
-                * 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 = nfsd_setuser_and_check_port(rqstp, exp);
-               if (error)
-                       goto out;
        }
+       dentry = fhp->fh_dentry;
+       exp = fhp->fh_export;
+       /*
+        * We still have to do all these permission checks, even when
+        * fh_dentry is already set:
+        *      - fh_verify may be called multiple times with different
+        *        "access" arguments (e.g. nfsd_proc_create calls
+        *        fh_verify(...,NFSD_MAY_EXEC) first, then later (in
+        *        nfsd_create) calls fh_verify(...,NFSD_MAY_CREATE).
+        *      - in the NFSv4 case, the filehandle may have been filled
+        *        in by fh_compose, and given a dentry, but further
+        *        compound operations performed with that filehandle
+        *        still need permissions checks.  In the worst case, a
+        *        mountpoint crossing may have changed the export
+        *        options, and we may now need to use a different uid
+        *        (for example, if different id-squashing options are in
+        *        effect on the new filesystem).
+        */
+       error = nfsd_setuser_and_check_port(rqstp, exp);
+       if (error)
+               goto out;
 
        error = nfsd_mode_check(rqstp, dentry->d_inode->i_mode, type);
        if (error)