[PATCH] crypto: af_alg - Work around empty control messages without MSG_MORE

[Herbert Xu]

The iwd daemon uses libell which sets up the skcipher operation with
two separate control messages.  This is fine by itself but the first
control message is sent without MSG_MORE.  This means that the first
control message is interpreted as an empty request.

While libell should be fixed to use MSG_MORE where appropriate, this
patch works around the bug in the kernel so that existing binaries
continue to work.

We will print a warning however.

Reported-by: Caleb Jorden <caljorden@xxxxxxxxxxx>
Fixes: f3c802a1f300 ("crypto: algif_aead - Only wake up when...")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index a6f581ab200c..3da21cadc326 100644
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -16,6 +16,7 @@
 #include <linux/module.h>
 #include <linux/net.h>
 #include <linux/rwsem.h>
+#include <linux/sched.h>
 #include <linux/sched/signal.h>
 #include <linux/security.h>
 
@@ -846,8 +847,14 @@ int af_alg_sendmsg(struct socket *sock, struct msghdr *msg, size_t size,
 
 	lock_sock(sk);
 	if (ctx->init && (init || !ctx->more)) {
-		err = -EINVAL;
-		goto unlock;
+		if (ctx->used) {
+			err = -EINVAL;
+			goto unlock;
+		}
+
+		pr_info_once(
+			"%s sent an empty control message without MSG_MORE.\n",
+			current->comm);
 	}
 	ctx->init = true;
 
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt