Merge tag '9p-for-4.21' of git://github.com/martinetd/linux

Pull 9p updates from Dominique Martinet:
 "Missing prototype warning fix and a syzkaller fix when a 9p server
  advertises a too small msize"

* tag '9p-for-4.21' of git://github.com/martinetd/linux:
  9p/net: put a lower bound on msize
  net/9p: include trans_common.h to fix missing prototype warning.

net/9p/client.c

@@ -181,6 +181,12 @@ static int parse_opts(char *opts, struct p9_client *clnt)
 				ret = r;
 				continue;
 			}
+			if (option < 4096) {
+				p9_debug(P9_DEBUG_ERROR,
+					 "msize should be at least 4k\n");
+				ret = -EINVAL;
+				continue;
+			}
 			clnt->msize = option;
 			break;
 		case Opt_trans:
@@ -983,10 +989,18 @@ static int p9_client_version(struct p9_client *c)
 	else if (!strncmp(version, "9P2000", 6))
 		c->proto_version = p9_proto_legacy;
 	else {
+		p9_debug(P9_DEBUG_ERROR,
+			 "server returned an unknown version: %s\n", version);
 		err = -EREMOTEIO;
 		goto error;
 	}
 
+	if (msize < 4096) {
+		p9_debug(P9_DEBUG_ERROR,
+			 "server returned a msize < 4096: %d\n", msize);
+		err = -EREMOTEIO;
+		goto error;
+	}
 	if (msize < c->msize)
 		c->msize = msize;
 
@@ -1043,6 +1057,13 @@ struct p9_client *p9_client_create(const char *dev_name, char *options)
 	if (clnt->msize > clnt->trans_mod->maxsize)
 		clnt->msize = clnt->trans_mod->maxsize;
 
+	if (clnt->msize < 4096) {
+		p9_debug(P9_DEBUG_ERROR,
+			 "Please specify a msize of at least 4k\n");
+		err = -EINVAL;
+		goto free_client;
+	}
+
 	err = p9_client_version(clnt);
 	if (err)
 		goto close_trans;

net/9p/trans_common.c

@@ -14,6 +14,7 @@
 
 #include <linux/mm.h>
 #include <linux/module.h>
+#include "trans_common.h"
 
 /**
  *  p9_release_pages - Release pages after the transaction.