From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 20 Apr 2016 21:56:45 +0000 (-0400)
Subject: Fix: lib_ring_buffer_copy_from_user_inatomic error handling
X-Git-Tag: v2.9.0-rc1~85
X-Git-Url: http://git.liburcu.org/?p=lttng-modules.git;a=commitdiff_plain;h=d87a9f0376535ea0ab125f2f0cfc6ce6e325c0c1

Fix: lib_ring_buffer_copy_from_user_inatomic error handling

It should treat nonzero return value of
lib_ring_buffer_do_copy_from_user_inatomic() as errors, 0 as success.

It is currently unused by the instrumentation.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/lib/ringbuffer/backend.h b/lib/ringbuffer/backend.h
index c0142071..b908ed06 100644
--- a/lib/ringbuffer/backend.h
+++ b/lib/ringbuffer/backend.h
@@ -334,8 +334,7 @@ void lib_ring_buffer_copy_from_user_inatomic(const struct lib_ring_buffer_config
 			rpages->p[index].virt + (offset & ~PAGE_MASK),
 			src, len);
 		if (unlikely(ret > 0)) {
-			len -= (pagecpy - ret);
-			offset += (pagecpy - ret);
+			/* Copy failed. */
 			goto fill_buffer;
 		}
 	} else {
diff --git a/lib/ringbuffer/backend_internal.h b/lib/ringbuffer/backend_internal.h
index d18967d6..16001776 100644
--- a/lib/ringbuffer/backend_internal.h
+++ b/lib/ringbuffer/backend_internal.h
@@ -451,6 +451,8 @@ do {								\
 /*
  * We use __copy_from_user_inatomic to copy userspace data since we already
  * did the access_ok for the whole range.
+ *
+ * Return 0 if OK, nonzero on error.
  */
 static inline
 unsigned long lib_ring_buffer_do_copy_from_user_inatomic(void *dest,
diff --git a/lib/ringbuffer/ring_buffer_backend.c b/lib/ringbuffer/ring_buffer_backend.c
index f34c7ccc..451ce23b 100644
--- a/lib/ringbuffer/ring_buffer_backend.c
+++ b/lib/ringbuffer/ring_buffer_backend.c
@@ -693,8 +693,7 @@ void _lib_ring_buffer_copy_from_user_inatomic(struct lib_ring_buffer_backend *bu
 							+ (offset & ~PAGE_MASK),
 							src, pagecpy) != 0;
 		if (ret > 0) {
-			offset += (pagecpy - ret);
-			len -= (pagecpy - ret);
+			/* Copy failed. */
 			_lib_ring_buffer_memset(bufb, offset, 0, len, 0);
 			break; /* stop copy */
 		}