Do not fence connections without valid greeting.

There is no reason to fence any connection that hasn't sent a valid
greeting, since they haven't progressed far enough for it to make
sense.

We remove the connection from the list of accepted clients, which then
removes the need for fencing, and the server won't need to restart.

Adds a test script that makes sure that we didn't actually restart the
server while this was happening.

Signed-off-by: Auke Kok <auke.kok@versity.com>

ReleaseNotes.md

@@ -1,6 +1,27 @@
 Versity ScoutFS Release Notes
 =============================
 
+---
+v1.25
+\
+*Jun 3, 2025*
+
+Fix a bug that could cause indefinite retries of failed client commits.
+Under specific error conditions the client and server's understanding of
+the current client commit could get out of sync.  The client would retry
+commits indefinitely that could never succeed.  This manifested as
+infinite "critical transaction commit failure" messages in the kernel
+log on the client and matching "error <nr> committing client logs" on
+the server.
+
+Fix a bug in a specific case of server error handling that could result
+in sending references to unwritten blocks to the client.  The client
+would try to read blocks that hadn't been written and return spurious
+errors.  This was seen under low free space conditions on the server and
+resulted in error messages with error code 116 (The errno enum for
+ESTALE, the client's indication that it couldn't read the blocks that it
+expected.)
+
 ---
 v1.24
 \

kmod/src/net.c

@@ -1278,6 +1278,17 @@ restart:
 			set_conn_fl(acc, reconn_freeing);
 			spin_unlock(&conn->lock);
 			if (!test_conn_fl(conn, shutting_down)) {
+				/*
+				 * If we haven't seen a vg for this connection, don't bother fencing
+				 * it - instead just drop it. If this was a real client, it will try
+				 * again to connect.
+				 */
+				if (!test_conn_fl(acc, valid_greeting)) {
+					/* delete the conn */
+					list_del_init(&acc->accepted_head);
+					goto restart;
+				}
+
 				scoutfs_info(sb, "client "SIN_FMT" reconnect timed out, fencing",
 					     SIN_ARG(&acc->last_peername));
 				ret = scoutfs_fence_start(sb, acc->rid,

tests/golden/portscan

@@ -0,0 +1,7 @@
+== empty packets
+Ncat: Connection refused.
+Ncat: Connection refused.
+== find portscan in connections
+
+== find portscan in connections
+

tests/sequence

@@ -57,4 +57,5 @@ archive-light-cycle.sh
 block-stale-reads.sh
 inode-deletion.sh
 renameat2-noreplace.sh
+portscan.sh
 xfstests.sh

tests/tests/portscan.sh

@@ -0,0 +1,24 @@
+#
+# portscan tests - assure malformed packets do not cause issues
+#
+
+t_require_commands scoutfs nc
+
+echo "== empty packets"
+sleep 1
+echo "    " | nc -p 33033 127.0.0.1 42000
+echo "    " | nc -p 33133 127.0.0.1 42001
+echo "    " | nc -p 33233 127.0.0.1 42002
+
+echo "== find portscan in connections"
+L=$(grep 'peer 127.0.0.1:33.33' /sys/kernel/debug/scoutfs/*/connections)
+echo $L
+
+# wait for fencing timeout (20s)
+sleep 30
+
+echo "== find portscan in connections"
+L=$(grep 'peer 127.0.0.1:33.33' /sys/kernel/debug/scoutfs/*/connections)
+echo $L
+
+t_pass