[PATCH] NFS: Change default behavior when "sec=" is not specified by user

[Chuck Lever <chuck.lever@oracle.com>]

Currently the kernel's MNT client always uses AUTH_UNIX if no "sec="
mount option was specified.  In the interest of conforming more
closely to RFC 2623, teach the MNT client to use the first flavor on
the server's returned authflavor list instead of AUTH_UNIX, if "sec="
was not specified.

When the user does not specify "sec=" :

 o  For NFSv2 and NFSv4: the default is always AUTH_UNIX (unchanged).

 o  For NFSv3: if the server does not return an auth flavor list, use
    AUTH_UNIX by default; if the server does return a list, use the
    first entry on the list by default.

See http://marc.info/?t=125075305400001&r=1&w=2 .

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---

Trond, Bruce-

Based on last week's e-mail discussion, maybe this should also be
included in 2.6.32?

 fs/nfs/super.c                  |   38 ++++++++++++++++++++++++++------------
 include/linux/sunrpc/msg_prot.h |    2 ++
 2 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index bde444b..5165847 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -1380,19 +1380,25 @@ static int nfs_walk_authlist(struct nfs_parsed_mount_data *args,
 	 * succeed), revert to pre-2.6.32 behavior (no checking)
 	 * if the returned flavor list is empty.
 	 */
-	if (server_authlist_len == 0)
+	if (server_authlist_len == 0) {
+		if (args->auth_flavors[0] == RPC_AUTH_UNSPEC)
+			args->auth_flavors[0] = RPC_AUTH_UNIX;
 		return 0;
+	}
 
 	/*
-	 * We avoid sophisticated negotiating here, as there are
-	 * plenty of cases where we can get it wrong, providing
-	 * either too little or too much security.
-	 *
 	 * RFC 2623, section 2.7 suggests we SHOULD prefer the
-	 * flavor listed first.  However, some servers list
-	 * AUTH_NULL first.  Our caller plants AUTH_SYS, the
-	 * preferred default, in args->auth_flavors[0] if user
-	 * didn't specify sec= mount option.
+	 * first flavor on the list if the user did not request
+	 * a specific flavor.
+	 */
+	if (args->auth_flavors[0] == RPC_AUTH_UNSPEC) {
+		args->auth_flavors[0] = request->auth_flavs[0];
+		return 0;
+	}
+
+	/*
+	 * Otherwise, check if the user-specified flavor is on the
+	 * server's list, and fail the mount if it is not found.
 	 */
 	for (i = 0; i < args->auth_flavor_len; i++)
 		for (j = 0; j < server_authlist_len; j++)
@@ -1467,8 +1473,12 @@ static int nfs_try_mount(struct nfs_parsed_mount_data *args,
 	/*
 	 * MNTv1 (NFSv2) does not support auth flavor negotiation.
 	 */
-	if (args->mount_server.version != NFS_MNT3_VERSION)
+	if (args->mount_server.version != NFS_MNT3_VERSION) {
+		if (args->auth_flavors[0] == RPC_AUTH_UNSPEC)
+			args->auth_flavors[0] = RPC_AUTH_UNIX;
 		return 0;
+	}
+
 	return nfs_walk_authlist(args, &request);
 }
 
@@ -1644,7 +1654,7 @@ static int nfs_validate_mount_data(void *options,
 	args->mount_server.port	= NFS_UNSPEC_PORT;
 	args->nfs_server.port	= NFS_UNSPEC_PORT;
 	args->nfs_server.protocol = XPRT_TRANSPORT_TCP;
-	args->auth_flavors[0]	= RPC_AUTH_UNIX;
+	args->auth_flavors[0]	= RPC_AUTH_UNSPEC;
 	args->auth_flavor_len	= 1;
 	args->minorversion	= 0;
 
@@ -1703,6 +1713,7 @@ static int nfs_validate_mount_data(void *options,
 		args->namlen		= data->namlen;
 		args->bsize		= data->bsize;
 
+		args->auth_flavors[0] = RPC_AUTH_UNIX;
 		if (data->flags & NFS_MOUNT_SECFLAVOUR)
 			args->auth_flavors[0] = data->pseudoflavor;
 		if (!args->nfs_server.hostname)
@@ -2323,6 +2334,8 @@ static int nfs4_validate_text_mount_data(void *options,
 			 "NFS4: Too many RPC auth flavours specified\n");
 		return -EINVAL;
 	}
+	if (args->auth_flavors[0] == RPC_AUTH_UNSPEC)
+		args->auth_flavors[0] = RPC_AUTH_UNIX;
 
 	if (args->client_address == NULL) {
 		dfprintk(MOUNT,
@@ -2358,7 +2371,7 @@ static int nfs4_validate_mount_data(void *options,
 	args->acdirmin		= NFS_DEF_ACDIRMIN;
 	args->acdirmax		= NFS_DEF_ACDIRMAX;
 	args->nfs_server.port	= NFS_UNSPEC_PORT;
-	args->auth_flavors[0]	= RPC_AUTH_UNIX;
+	args->auth_flavors[0]	= RPC_AUTH_UNSPEC;
 	args->auth_flavor_len	= 1;
 	args->minorversion	= 0;
 
@@ -2374,6 +2387,7 @@ static int nfs4_validate_mount_data(void *options,
 		if (!nfs_verify_server_address(sap))
 			goto out_no_address;
 
+		args->auth_flavors[0] = RPC_AUTH_UNIX;
 		if (data->auth_flavourlen) {
 			if (data->auth_flavourlen > 1)
 				goto out_inval_auth;
diff --git a/include/linux/sunrpc/msg_prot.h b/include/linux/sunrpc/msg_prot.h
index 77e6248..7d6d3ed 100644
--- a/include/linux/sunrpc/msg_prot.h
+++ b/include/linux/sunrpc/msg_prot.h
@@ -35,6 +35,8 @@ enum rpc_auth_flavors {
 	RPC_AUTH_GSS_SPKM  = 390009,
 	RPC_AUTH_GSS_SPKMI = 390010,
 	RPC_AUTH_GSS_SPKMP = 390011,
+	/* flavor was unspecified: */
+	RPC_AUTH_UNSPEC = 0xffffffff,
 };
 
 /* Maximum size (in bytes) of an rpc credential or verifier */