NFS: Check lengths more thoroughly in NFS4 readdir XDR decode

Check the bounds of length specifiers more thoroughly in the XDR decoding of
NFS4 readdir reply data.

Currently, if the server returns a bitmap or attr length that causes the
current decode point pointer to wrap, this could go undetected (consider a
small "negative" length on a 32-bit machine).

Also add a check into the main XDR decode handler to make sure that the amount
of data is a multiple of four bytes (as specified by RFC-1014).  This makes
sure that we can do u32* pointer subtraction in the NFS client without risking
an undefined result (the result is undefined if the pointers are not correctly
aligned with respect to one another).

Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
(cherry picked from 5861fddd64a7eaf7e8b1a9997455a24e7f688092 commit)

1 files changed, 11 insertions, 0 deletions

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index d9eac7069101..3e19d321067a 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -1181,6 +1181,17 @@ call_verify(struct rpc_task *task)
         u32     *p = iov->iov_base, n;
         int error = -EACCES;
 
+        if ((task->tk_rqstp->rq_rcv_buf.len & 3) != 0) {
+                /* RFC-1014 says that the representation of XDR data must be a
+                 * multiple of four bytes
+                 * - if it isn't pointer subtraction in the NFS client may give
+                 *   undefined results
+                 */
+                printk(KERN_WARNING
+                       "call_verify: XDR representation not a multiple of"
+                       " 4 bytes: 0x%x\n", task->tk_rqstp->rq_rcv_buf.len);
+                goto out_eio;
+        }
         if ((len -= 3) < 0)
                 goto out_overflow;
         p += 1; /* skip XID */