[PATCH 3/3] tracing/probes: Fix return value when "(fault)" is injected

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

When the "(fault)" is injected, the return value of fetch_store_string*()
should be the length of the "(fault)", but an error code is returned.
Fix it to return the correct length and update the data_loc according the
updated length.
This needs to update a ftracetest test case, which expects trace output
to appear as '(fault)' instead of '"(fault)"'.

Fixes: 2e9906f84fc7 ("tracing: Add "(fault)" name injection to kernel probes")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
 kernel/trace/trace_probe_kernel.h                  |   17 +++++++----------
 .../ftrace/test.d/kprobe/kprobe_args_user.tc       |    2 +-
 2 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/kernel/trace/trace_probe_kernel.h b/kernel/trace/trace_probe_kernel.h
index c4e1d4c03a85..63d90fe4eb87 100644
--- a/kernel/trace/trace_probe_kernel.h
+++ b/kernel/trace/trace_probe_kernel.h
@@ -48,14 +48,15 @@ fetch_store_strlen(unsigned long addr)
 	return (ret < 0) ? strlen(FAULT_STRING) + 1 : len;
 }
 
-static nokprobe_inline void set_data_loc(int ret, void *dest, void *__dest, void *base, int len)
+static nokprobe_inline int set_data_loc(int ret, void *dest, void *__dest, void *base, int len)
 {
-	if (ret >= 0) {
-		*(u32 *)dest = make_data_loc(ret, __dest - base);
-	} else {
+	if (ret < 0) {
 		strscpy(__dest, FAULT_STRING, len);
 		ret = strlen(__dest) + 1;
 	}
+
+	*(u32 *)dest = make_data_loc(ret, __dest - base);
+	return ret;
 }
 
 /*
@@ -76,9 +77,7 @@ fetch_store_string_user(unsigned long addr, void *dest, void *base)
 	__dest = get_loc_data(dest, base);
 
 	ret = strncpy_from_user_nofault(__dest, uaddr, maxlen);
-	set_data_loc(ret, dest, __dest, base, maxlen);
-
-	return ret;
+	return set_data_loc(ret, dest, __dest, base, maxlen);
 }
 
 /*
@@ -107,9 +106,7 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
 	 * probing.
 	 */
 	ret = strncpy_from_kernel_nofault(__dest, (void *)addr, maxlen);
-	set_data_loc(ret, dest, __dest, base, maxlen);
-
-	return ret;
+	return set_data_loc(ret, dest, __dest, base, maxlen);
 }
 
 static nokprobe_inline int
diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc
index d25d01a19778..8dcc0b29bd36 100644
--- a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc
+++ b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc
@@ -29,6 +29,6 @@ echo 1 > events/kprobes/myevent/enable
 ln -s foo $TMPDIR/bar
 echo 0 > events/kprobes/myevent/enable
 
-grep myevent trace | grep -q 'path=(fault) path2=(fault)'
+grep myevent trace | grep -q 'path="*(fault)"* path2="*(fault)"*'
 
 exit 0