Fix: ensure userspace accesses are done with _inatomic

[lttng-modules.git] / probes / lttng-probe-user.c

diff --git a/probes/lttng-probe-user.c b/probes/lttng-probe-user.c
new file mode 100644 (file)
index 0000000..94ecf2f
--- /dev/null
+++ b/probes/lttng-probe-user.c
@@ -0,0 +1,54 @@
+/*
+ * lttng-probe-user.c
+ *
+ * Copyright (C) 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; only
+ * version 2.1 of the License.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <linux/uaccess.h>
+#include "lttng-probe-user.h"
+
+/*
+ * Calculate string length. Include final null terminating character if there is
+ * one, or ends at first fault. Disabling page faults ensures that we can safely
+ * call this from pretty much any context, including those where the caller
+ * holds mmap_sem, or any lock which nests in mmap_sem.
+ */
+long lttng_strlen_user_inatomic(const char *addr)
+{
+       long count = 0;
+       mm_segment_t old_fs = get_fs();
+
+       set_fs(KERNEL_DS);
+       pagefault_disable();
+       for (;;) {
+               char v;
+               long ret;
+
+               ret = __copy_from_user_inatomic(&v,
+                       (__force const char __user *)(addr),
+                       sizeof(v));
+               if (unlikely(ret == -EFAULT))
+                       break;
+               count++;
+               if (unlikely(!v))
+                       break;
+               addr++;
+       }
+       pagefault_enable();
+       set_fs(old_fs);
+       return count;
+}