Extcap: Create our fifo in a temporary directory.

Instead of creating a temp file, unlinking it, and creating a fifo with
the same name, add create_tempdir() so that we can create a temporary
directory and create a fifo inside that.

This should avoid a race condition in Carbon Black Cloud antivirus,
which if the timing is right, will stat the initial temporary *file*,
miss the fact that it's been replaced with a *fifo*, and open and steal
data^W^W read from it, leaving dumpcap to contend with the truncated
remains.

Adding the unexpected magic number to cap_pipe_open_live()'s error
message helped to debug this. Leave it in since it's handy to have in
that case.

Ping #15587

4 files changed, 74 insertions, 34 deletions

diff --git a/dumpcap.c b/dumpcap.c
index 5ac209015e..e09f27d59d 100644
--- a/dumpcap.c
+++ b/dumpcap.c
@@ -1850,7 +1850,7 @@ cap_pipe_open_live(char *pipename,
         /* Not a pcapng file, and either not a pcap type we know about
            or not a pcap file, either. */
         snprintf(errmsg, (gulong)errmsgl,
-                   "Data written to the pipe is neither in a supported pcap format nor in pcapng format.");
+                   "File type is neither a supported pcap nor pcapng format. (magic = 0x%08x)", magic);
         snprintf(secondary_errmsg, (gulong)secondary_errmsgl, "%s",
                    not_our_bug);
         goto error;
diff --git a/extcap.c b/extcap.c
index ee7e469f45..e5794a3c3e 100644
--- a/extcap.c
+++ b/extcap.c
@@ -1354,6 +1354,8 @@ gboolean extcap_session_stop(capture_session *cap_session)
             }
             /* the fifo will not be freed here, but with the other capture_opts in capture_sync */
             ws_unlink(interface_opts->extcap_fifo);
+            get_dirname(interface_opts->extcap_fifo);
+            rmdir(interface_opts->extcap_fifo);
             interface_opts->extcap_fifo = NULL;
         }
         if (interface_opts->extcap_control_in && file_exists(interface_opts->extcap_control_in))
@@ -1661,33 +1663,27 @@ static gboolean extcap_create_pipe(const gchar *ifname, gchar **fifo, HANDLE *ha
 #else
 static gboolean extcap_create_pipe(const gchar *ifname, gchar **fifo, const gchar *temp_dir, const gchar *pipe_prefix)
 {
-    gchar *temp_name = NULL;
-    int fd = 0;
+    gchar *subdir_tmpl = g_strdup_printf("%s_%s_XXXXXX", pipe_prefix, ifname);
+    gchar *temp_subdir = create_tempdir(temp_dir, subdir_tmpl, NULL);
 
-    gchar *pfx = g_strconcat(pipe_prefix, "_", ifname, NULL);
-    if ((fd = create_tempfile(temp_dir, &temp_name, pfx, NULL, NULL)) < 0)
+    g_free(subdir_tmpl);
+    if (temp_subdir == NULL)
     {
-        g_free(pfx);
         return FALSE;
     }
-    g_free(pfx);
 
-    ws_close(fd);
+    gchar *fifo_path = g_build_path(G_DIR_SEPARATOR_S, temp_subdir, "fifo", NULL);
+    g_free(temp_subdir);
 
-    ws_debug("Extcap - Creating fifo: %s", temp_name);
+    ws_debug("Extcap - Creating fifo: %s", fifo_path);
 
-    if (file_exists(temp_name))
+    if (mkfifo(fifo_path, 0600) == 0)
     {
-        ws_unlink(temp_name);
-    }
-
-    if (mkfifo(temp_name, 0600) == 0)
-    {
-        *fifo = temp_name;
+        *fifo = fifo_path;
     }
     else
     {
-        g_free(temp_name);
+        g_free(fifo_path);
     }
     return TRUE;
 }
diff --git a/wsutil/tempfile.c b/wsutil/tempfile.c
index f93f96d538..165269f54f 100644
--- a/wsutil/tempfile.c
+++ b/wsutil/tempfile.c
@@ -15,6 +15,28 @@
 #include "tempfile.h"
 #include "file_util.h"
 
+static char *
+sanitize_prefix(const char *prefix)
+{
+  if (!prefix) {
+      return NULL;
+  }
+
+  /* The characters in "delimiters" come from:
+   * https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#naming-conventions.
+   * Add to the list as necessary for other OS's.
+   */
+  const gchar *delimiters = "<>:\"/\\|?*"
+    "\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a"
+    "\x0b\x0c\x0d\x0e\x0f\x10\x11\x12\x13\x14"
+    "\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f";
+
+  /* Sanitize the prefix to resolve bug 7877 */
+  char *safe_prefx = g_strdup(prefix);
+  safe_prefx = g_strdelimit(safe_prefx, delimiters, '-');
+  return safe_prefx;
+}
+
  /**
  * Create a tempfile with the given prefix (e.g. "wireshark"). The path
  * is created using g_file_open_tmp.
@@ -32,22 +54,7 @@ int
 create_tempfile(const char *tempdir, gchar **namebuf, const char *pfx, const char *sfx, GError **err)
 {
   int fd;
-  gchar *safe_pfx = NULL;
-
-  if (pfx) {
-    /* The characters in "delimiters" come from:
-     * https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#naming-conventions.
-     * Add to the list as necessary for other OS's.
-     */
-    const gchar *delimiters = "<>:\"/\\|?*"
-      "\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a"
-      "\x0b\x0c\x0d\x0e\x0f\x10\x11\x12\x13\x14"
-      "\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f";
-
-    /* Sanitize the pfx to resolve bug 7877 */
-    safe_pfx = g_strdup(pfx);
-    safe_pfx = g_strdelimit(safe_pfx, delimiters, '-');
-  }
+  gchar *safe_pfx = sanitize_prefix(pfx);
 
   if (tempdir == NULL || tempdir[0] == '\0') {
     /* Use OS default tempdir behaviour */
@@ -107,6 +114,31 @@ create_tempfile(const char *tempdir, gchar **namebuf, const char *pfx, const cha
   return fd;
 }
 
+char *
+create_tempdir(const gchar *parent_dir, const char *tmpl, GError **err)
+{
+  if (parent_dir == NULL || parent_dir[0] == '\0') {
+      parent_dir = g_get_tmp_dir();
+  }
+
+  gchar *safe_pfx = sanitize_prefix(tmpl);
+  if (safe_pfx == NULL) {
+    safe_pfx = g_strdup("wireshark_XXXXXX");
+  }
+
+  char *temp_subdir = g_build_path(G_DIR_SEPARATOR_S, parent_dir, safe_pfx, NULL);
+  g_free(safe_pfx);
+  if (g_mkdtemp(temp_subdir) == NULL)
+  {
+      g_free(temp_subdir);
+      g_set_error_literal(err, G_FILE_ERROR,
+          g_file_error_from_errno(errno), g_strerror(errno));
+      return FALSE;
+  }
+
+  return temp_subdir;
+}
+
 /*
  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
  *
diff --git a/wsutil/tempfile.h b/wsutil/tempfile.h
index 70031b5419..65e0c59898 100644
--- a/wsutil/tempfile.h
+++ b/wsutil/tempfile.h
@@ -27,7 +27,7 @@ extern "C" {
  *
  * @param tempdir [in] If not NULL, the directory in which to create the file.
  * @param namebuf [in,out] If not NULL, receives the full path of the temp file.
- *                Must be freed.
+ *                Must be g_freed.
  * @param pfx [in] A prefix for the temporary file.
  * @param sfx [in] A file extension for the temporary file. NULL can be passed
  *                 if no file extension is needed
@@ -36,6 +36,18 @@ extern "C" {
  */
 WS_DLL_PUBLIC int create_tempfile(const gchar *tempdir, gchar **namebuf, const char *pfx, const char *sfx, GError **err);
 
+/**
+ * Create a tempfile with the given parent directory (e.g. "/my/private/tmp"). The path
+ * is created using g_mkdtemp.
+ *
+ * @param parent_dir [in] If not NULL, the parent directory in which to create the subdirectory,
+ *                        otherwise the system temporary directory is used.
+ * @param tmpl [in] A template for the temporary directory.
+ * @param err [out] Any error returned by g_mkdtemp. May be NULL.
+ * @return The full path of the temporary directory or NULL on error. Must be g_freed.
+ */
+WS_DLL_PUBLIC char *create_tempdir(const gchar *parent_dir, const char *tmpl, GError **err);
+
 #ifdef __cplusplus
 }
 #endif /* __cplusplus */