[PATCH] error out if signing was requested, but can't be fulfilled

[Jeff Layton <jlayton@redhat.com>]

Currently, if mount with a signing-enabled sec= option (e.g.
sec=ntlmi), the kernel does a warning printk if the server doesn't
support signing, and then proceeds without signatures.

This is probably OK for people that think to look at the ring buffer,
but seems wrong to me. If someone explicitly requests signing, we
should error out if that request can't be satisfied. They can then
reattempt the mount without signing if that's ok.

Is there any reason not to do something like the following patch?

Signed-off-by: Jeff Layton <jlayton@redhat.com>

diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index 4a2458e..c9cae48 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -650,6 +650,7 @@ signing_check:
 			(SECMODE_SIGN_ENABLED | SECMODE_SIGN_REQUIRED)) == 0) {
 			cERROR(1,
 				("signing required but server lacks support"));
+			rc = -EOPNOTSUPP;
 		} else
 			server->secMode |= SECMODE_SIGN_REQUIRED;
 	} else {