[PATCH 3.16 131/366] tracing/uprobe_event: Fix strncpy corner case

[Ben Hutchings]

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

commit 50268a3d266ecfdd6c5873d62b2758d9732fc598 upstream.

Fix string fetch function to terminate with NUL.
It is OK to drop the rest of string.

Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Song Liu <songliubraving@xxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: security@xxxxxxxxxx
Cc: èéé <long7573@xxxxxxx>
Fixes: 5baaa59ef09e ("tracing/probes: Implement 'memory' fetch method for uprobes")
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 kernel/trace/trace_uprobe.c | 2 ++
 1 file changed, 2 insertions(+)

--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -149,6 +149,8 @@ static void FETCH_FUNC_NAME(memory, stri
 		return;
 
 	ret = strncpy_from_user(dst, src, maxlen);
+	if (ret == maxlen)
+		dst[--ret] = '\0';
 
 	if (ret < 0) {	/* Failed to fetch string */
 		((u8 *)get_rloc_data(dest))[0] = '\0';