[PATCH 3.12 075/111] svcrpc: fix potential GSSX_ACCEPT_SEC_CONTEXT decoding failures

[Jiri Slaby]

From: Scott Mayhew <smayhew@xxxxxxxxxx>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 9507271d960a1911a51683888837d75c171cd91f upstream.

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@xxxxxxxxxx>
Reviewed-by: Simo Sorce <simo@xxxxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 net/sunrpc/auth_gss/gss_rpc_xdr.c | 23 ++++++++++++++++-------
 1 file 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 f0f78c5f1c7d..e0062c544ac8 100644
--- a/net/sunrpc/auth_gss/gss_rpc_xdr.c
+++ b/net/sunrpc/auth_gss/gss_rpc_xdr.c
@@ -794,20 +794,26 @@ 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;
 	}
@@ -815,11 +821,11 @@ 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;
 	}
@@ -827,14 +833,17 @@ 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;
 }
-- 
2.4.2

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