[linux-cifs-client] [PATCH 2/2] cifs: add mechListMIC string to SPNEGO upcall key description

[Jeff Layton]

Signed-off-by: Jeff Layton <jlayton at redhat.com>
---
 fs/cifs/cifs_spnego.c |   16 +++++++++++++++-
 1 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/fs/cifs/cifs_spnego.c b/fs/cifs/cifs_spnego.c
index 117ef4b..ae697a0 100644
--- a/fs/cifs/cifs_spnego.c
+++ b/fs/cifs/cifs_spnego.c
@@ -88,7 +88,9 @@ cifs_get_spnego_key(struct cifsSesInfo *sesInfo)
 		   5 /* len of ";ipv4=" */ + MAX_IPV6_ADDR_LEN +
 		   MAX_MECH_STR_LEN +
 		   7 /* len of ";uid=0x" */ + (sizeof(uid_t) * 2) +
-		   6 /* len of ";user=" */ + strlen(sesInfo->userName) + 1;
+		   6 /* len of ";user=" */ + strlen(sesInfo->userName) +
+		   5 /* len of ";mic=" */ + strlen(server->mechListMIC) +
+		   1 /* terminating NULL */;
 
 	spnego_key = ERR_PTR(-ENOMEM);
 	description = kzalloc(desc_len, GFP_KERNEL);
@@ -128,6 +130,18 @@ cifs_get_spnego_key(struct cifsSesInfo *sesInfo)
 	dp = description + strlen(description);
 	sprintf(dp, ";user=%s", sesInfo->userName);
 
+	/*
+	 * Early MS KRB5 implementations had a bug that caused them to
+	 * hijack the mechListMIC field and stuff the server's principal
+	 * in it. Later versions have carried this bug for compatibility
+	 * reasons. We pass this string to the upcall in case it turns
+	 * out to be useful in situations where DNS isn't correct.
+	 */
+	if (server->mechListMIC) {
+		dp = description + strlen(description);
+		sprintf(dp, ";mic=%s", server->mechListMIC);
+	}
+
 	cFYI(1, ("key description = %s", description));
 	spnego_key = request_key(&cifs_spnego_key_type, description, "");
 
-- 
1.5.5.1