svcrpc: fix potential GSSX_ACCEPT_SEC_CONTEXT decoding failures

In an environment where the KDC is running Active Directory, the
exported composite name field returned in the context could be large
enough to span a page boundary.  Attaching a scratch buffer to the
decoding xdr_stream helps deal with those cases.

The case where we saw this was actually due to behavior that's been
fixed in newer gss-proxy versions, but we're fixing it here too.

Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Cc: stable@vger.kernel.org
Reviewed-by: Simo Sorce <simo@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 16 insertions, 7 deletions

diff --git a/net/sunrpc/auth_gss/gss_rpc_xdr.c b/net/sunrpc/auth_gss/gss_rpc_xdr.c
index 1ec19f6f0c2b..eeeba5adee6d 100644
--- a/net/sunrpc/auth_gss/gss_rpc_xdr.c
+++ b/net/sunrpc/auth_gss/gss_rpc_xdr.c
@@ -793,20 +793,26 @@ int gssx_dec_accept_sec_context(struct rpc_rqst *rqstp,
 {
         u32 value_follows;
         int err;
+        struct page *scratch;
+
+        scratch = alloc_page(GFP_KERNEL);
+        if (!scratch)
+                return -ENOMEM;
+        xdr_set_scratch_buffer(xdr, page_address(scratch), PAGE_SIZE);
 
         /* res->status */
         err = gssx_dec_status(xdr, &res->status);
         if (err)
-                return err;
+                goto out_free;
 
         /* res->context_handle */
         err = gssx_dec_bool(xdr, &value_follows);
         if (err)
-                return err;
+                goto out_free;
         if (value_follows) {
                 err = gssx_dec_ctx(xdr, res->context_handle);
                 if (err)
-                        return err;
+                        goto out_free;
         } else {
                 res->context_handle = NULL;
         }
@@ -814,11 +820,11 @@ int gssx_dec_accept_sec_context(struct rpc_rqst *rqstp,
         /* res->output_token */
         err = gssx_dec_bool(xdr, &value_follows);
         if (err)
-                return err;
+                goto out_free;
         if (value_follows) {
                 err = gssx_dec_buffer(xdr, res->output_token);
                 if (err)
-                        return err;
+                        goto out_free;
         } else {
                 res->output_token = NULL;
         }
@@ -826,14 +832,17 @@ int gssx_dec_accept_sec_context(struct rpc_rqst *rqstp,
         /* res->delegated_cred_handle */
         err = gssx_dec_bool(xdr, &value_follows);
         if (err)
-                return err;
+                goto out_free;
         if (value_follows) {
                 /* we do not support upcall servers sending this data. */
-                return -EINVAL;
+                err = -EINVAL;
+                goto out_free;
         }
 
         /* res->options */
         err = gssx_dec_option_array(xdr, &res->options);
 
+out_free:
+        __free_page(scratch);
         return err;
 }