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>

diff --git a/net/sunrpc/auth_gss/gss_rpc_xdr.c b/net/sunrpc/auth_gss/gss_rpc_xdr.c
index 1ec19f6..eeeba5a 100644 (file)
--- 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;
 }