Re: SUNRPC: Add RPC based upcall mechanism for RPCGSS auth

["J. Bruce Fields" <bfields@redhat.com>]

On Mon, May 06, 2013 at 11:54:53AM -0400, Simo Sorce wrote:
> On Mon, 2013-05-06 at 18:44 +0300, Dan Carpenter wrote:
> > Hello Simo Sorce,
> > 
> > The patch 1d658336b05f: "SUNRPC: Add RPC based upcall mechanism for 
> > RPCGSS auth" from May 25, 2012, leads to the following warning:
> > "net/sunrpc/auth_gss/gss_rpc_xdr.c:30 gssx_check_pointer()
> > 	 warn: signedness bug returning '(-28)'"
> > 
> > net/sunrpc/auth_gss/gss_rpc_xdr.c
> >     24  static bool gssx_check_pointer(struct xdr_stream *xdr)
> >     25  {
> >     26          __be32 *p;
> >     27  
> >     28          p = xdr_reserve_space(xdr, 4);
> >     29          if (unlikely(p == NULL))
> >     30                  return -ENOSPC;
> >                                ^^^^^^^
> > This is casted implicitly to "true".  Functions named "check" are a bad
> > idea anyways because it's not clear what the return value will be.  It's
> > better to use "gssx_pointer_ok()" or "valid" where obviously true means
> > that the pointer is ok.
> > 
> >     31          return *p?true:false;
> > 
> > We just reserved "*p" so doesn't this point to uninitialized data?  It
> > points to a __be32.  So we're not really checking a pointer we're
> > checking that __be32 is non-zero.
> > 
> >     32  }
> > 
> > regards,
> > dan carpenter
> 
> Dan,
> thanks a lot for pointing this one out.

Yes, thanks!

> Bruce,
> we should fix it in 3.10 if we can make it.

Agreed.  Probably the following attempt to decode will fail with an
-ENOSPC anyway, but this is ugly at least.

> probably easiest way is to kill lines 29/30 and do:
> return (p && *p) ? true : false;
> 
> It would be also ok to change the name to gssx_pointer_is_valid() I
> guess.

It still seems a little yuch to lump a decoding failure with a succesful
decode of a particular value....

How about just killing gssx_check_pointer, as follows.  Admittedly it's
a bit verbose, but it's straightforward.  Any objections?

--b.

commit fb43f11c666a4f99f23f0be4fa528dcd288c0da2
Author: J. Bruce Fields <bfields@redhat.com>
Date:   Tue May 7 17:45:20 2013 -0400

    SUNRPC: fix decoding of optional gss-proxy xdr fields
    
    The current code works, but sort of by accident: it obviously didn't
    intend the error return to be interpreted as "true".
    
    Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
    Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/net/sunrpc/auth_gss/gss_rpc_xdr.c b/net/sunrpc/auth_gss/gss_rpc_xdr.c
index a1e1b1a..357f613 100644
--- a/net/sunrpc/auth_gss/gss_rpc_xdr.c
+++ b/net/sunrpc/auth_gss/gss_rpc_xdr.c
@@ -21,16 +21,6 @@
 #include <linux/sunrpc/svcauth.h>
 #include "gss_rpc_xdr.h"
 
-static bool gssx_check_pointer(struct xdr_stream *xdr)
-{
-	__be32 *p;
-
-	p = xdr_reserve_space(xdr, 4);
-	if (unlikely(p == NULL))
-		return -ENOSPC;
-	return *p?true:false;
-}
-
 static int gssx_enc_bool(struct xdr_stream *xdr, int v)
 {
 	__be32 *p;
@@ -802,6 +792,7 @@ int gssx_dec_accept_sec_context(struct rpc_rqst *rqstp,
 				struct xdr_stream *xdr,
 				struct gssx_res_accept_sec_context *res)
 {
+	u32 value_follows;
 	int err;
 
 	/* res->status */
@@ -810,7 +801,10 @@ int gssx_dec_accept_sec_context(struct rpc_rqst *rqstp,
 		return err;
 
 	/* res->context_handle */
-	if (gssx_check_pointer(xdr)) {
+	err = gssx_dec_bool(xdr, &value_follows);
+	if (err)
+		return err;
+	if (value_follows) {
 		err = gssx_dec_ctx(xdr, res->context_handle);
 		if (err)
 			return err;
@@ -819,7 +813,10 @@ int gssx_dec_accept_sec_context(struct rpc_rqst *rqstp,
 	}
 
 	/* res->output_token */
-	if (gssx_check_pointer(xdr)) {
+	err = gssx_dec_bool(xdr, &value_follows);
+	if (err)
+		return err;
+	if (value_follows) {
 		err = gssx_dec_buffer(xdr, res->output_token);
 		if (err)
 			return err;
@@ -828,7 +825,10 @@ int gssx_dec_accept_sec_context(struct rpc_rqst *rqstp,
 	}
 
 	/* res->delegated_cred_handle */
-	if (gssx_check_pointer(xdr)) {
+	err = gssx_dec_bool(xdr, &value_follows);
+	if (err)
+		return err;
+	if (value_follows) {
 		/* we do not support upcall servers sending this data. */
 		return -EINVAL;
 	}