fix: deadlock in whisper, use-after-free in callbacks, log rotation, tail parsing

- Whisper: copy target client ref out of room lock before calling
  client_send, preventing lock-ordering inversion deadlock
- Channel callbacks: call ssh_remove_channel_callbacks before releasing
  refs to prevent use-after-free if a callback fires during cleanup
- Log rotation: rotate messages.log to messages.log.1 when it exceeds
  10 MiB, preventing unbounded growth on public servers
- tail -nN: accept both "tail -n5" and "tail -n 5" forms, matching
  standard Unix tail behavior

Closes #36

include/common.h

@@ -22,6 +22,7 @@
 #define MAX_EXEC_COMMAND_LEN 1024
 #define MAX_CLIENTS 64
 #define LOG_FILE "messages.log"
+#define MAX_LOG_SIZE (10 * 1024 * 1024)  /* 10 MiB */
 #define HOST_KEY_FILE "host_key"
 #define TNT_DEFAULT_STATE_DIR "."
 

src/message.c

@@ -227,7 +227,16 @@ int message_save(const message_t *msg) {
         rc = -1;
     }
 
+    /* Rotate if the log exceeds MAX_LOG_SIZE */
+    long file_size = ftell(fp);
     fclose(fp);
+
+    if (file_size > MAX_LOG_SIZE) {
+        char backup_path[PATH_MAX + 4];
+        snprintf(backup_path, sizeof(backup_path), "%s.1", log_path);
+        rename(log_path, backup_path);
+    }
+
     pthread_mutex_unlock(&g_message_file_lock);
     return rc;
 }

src/ssh_server.c

@@ -895,7 +895,7 @@ static int parse_tail_count(const char *args, int *count) {
         return 0;
     }
 
-    if (strncmp(args, "-n", 2) == 0 && isspace((unsigned char)args[2])) {
+    if (strncmp(args, "-n", 2) == 0) {
         args += 2;
         while (*args && isspace((unsigned char)*args)) {
             args++;
@@ -1171,21 +1171,28 @@ static void execute_command(client_t *client) {
                            "       w <username> <message>\n");
         } else {
             bool found = false;
+            client_t *target = NULL;
             pthread_rwlock_rdlock(&g_room->lock);
             for (int i = 0; i < g_room->client_count; i++) {
                 if (strcmp(g_room->clients[i]->username, target_name) == 0) {
-                    char whisper[MAX_MESSAGE_LEN];
-                    snprintf(whisper, sizeof(whisper),
-                             "\r\n\033[35m[whisper from %s]: %s\033[0m\r\n",
-                             client->username, rest);
-                    client_send(g_room->clients[i], whisper, strlen(whisper));
-                    g_room->clients[i]->redraw_pending = true;
+                    target = g_room->clients[i];
+                    client_addref(target);
                     found = true;
                     break;
                 }
             }
             pthread_rwlock_unlock(&g_room->lock);
 
+            if (target) {
+                char whisper[MAX_MESSAGE_LEN];
+                snprintf(whisper, sizeof(whisper),
+                         "\r\n\033[35m[whisper from %s]: %s\033[0m\r\n",
+                         client->username, rest);
+                client_send(target, whisper, strlen(whisper));
+                target->redraw_pending = true;
+                client_release(target);
+            }
+
             if (found) {
                 buffer_appendf(output, sizeof(output), &pos,
                                "Whisper sent to %s\n", target_name);
@@ -1649,6 +1656,12 @@ cleanup:
 
     release_ip_connection(client->client_ip);
 
+    /* Remove channel callbacks before releasing refs to prevent use-after-free
+     * if a callback fires between the two releases. */
+    if (client->channel && client->channel_cb) {
+        ssh_remove_channel_callbacks(client->channel, client->channel_cb);
+    }
+
     /* Release the callback reference (paired with addref before install_client_channel_callbacks) */
     client_release(client);