On Fri, Jan 09, 2015 at 04:30:45AM +0100, Stephan Mueller wrote:

Am Donnerstag, 8. Januar 2015, 22:09:31 schrieb Herbert Xu:

Hi Herbert,

quoted

On Wed, Jan 07, 2015 at 04:51:38PM +0100, Stephan Mueller wrote:

quoted

+		if (!aead_writable(sk)) {
+			/*
+			 * If there is more data to be expected, but we cannot
+			 * write more data, forcefully define that we do not
+			 * expect more data to invoke the AEAD operation. This
+			 * prevents a deadlock in user space.
+			 */
+			ctx->more = 0;

We should return EMSGSIZE here.  Also we should clear out the
existing data so that the socket may be reused again.

Is this really wise considering that we want to support a threaded caller? For 
example, one thread sends data and another reads data. For some reason, the 
reading thread is throttled or slower than the sender. Now, with the current 
solution, the sender is put on hold (i.e. throttled) until the reader can 
catch up. I.e. we have an automated synchronization between sender/receiver.

Thus, when we remove the wait here and return an error, the sender will be 
shut down and there is no synchronization of the reader/writer any more.

Note, the same applies to the very similar code in aead_sendpage too.

No, if we're in this case then something seriously wrong has
happened.  IOW the application writer has screwed up.  We're
not able to carry out the wish of user-space because of resource
limits on the socket.  Attempting to continue at this point will
only cause confusion.

So we should loudly declare that there was an error.

quoted

quoted

+	ctx->more = msg->msg_flags & MSG_MORE;
+	if (!ctx->more && !aead_sufficient_data(ctx))
+		err = -EINVAL;

Ditto, we should discard the data that's queued up.  Also perhaps
use EBADMSG instead of EINVAL.

Agreed that we should clear out the buffer. I will provide that in the next 
release for both, the sendmsg and sendpage implementations.

However, I am not sure whether using EBADMSG is a good idea. The error of 
EBADMSG in the kernel crypto API is only used for integrity errors of AEAD 
ciphers. But our error case here has nothing to do with the integrity error.

I would be fine with any other error number -- EMSGSIZE as you suggested 
above?

Sure.

Do you think whether such approach makes sense? If yes, which limit to the 
number of rsgl should we apply -- is ALG_MAX_PAGES good?

Yes I think your solution in v10 is fine.  The current kernel
AEAD interface isn't the best but we're stuck with it for the
time being so this is the best we can do.

Cheers,
-- 
Email: Herbert Xu [off-list ref]
Home Page: http://gondor.apana.org.au/~herbert/
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