[PATCH 3.2 100/185] tracing: Allow events to have NULL strings

Ben Hutchings
2013-12-29T02:32:53Z

From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

commit 4e58e54754dc1fec21c3a9e824bc108b05fdf46e upstream.

If an TRACE_EVENT() uses __assign_str() or __get_str on a NULL pointer
then the following oops will happen:

BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<c127a17b>] strlen+0x10/0x1a
*pde = 00000000 ^M
Oops: 0000 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.13.0-rc1-test+ #2
Hardware name: /DG965MQ, BIOS MQ96510J.86A.0372.2006.0605.1717 06/05/2006^M
task: f5cde9f0 ti: f5e5e000 task.ti: f5e5e000
EIP: 0060:[<c127a17b>] EFLAGS: 00210046 CPU: 1
EIP is at strlen+0x10/0x1a
EAX: 00000000 EBX: c2472da8 ECX: ffffffff EDX: c2472da8
ESI: c1c5e5fc EDI: 00000000 EBP: f5e5fe84 ESP: f5e5fe80
DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
CR0: 8005003b CR2: 00000000 CR3: 01f32000 CR4: 000007d0
Stack:
f5f18b90 f5e5feb8 c10687a8 0759004f 00000005 00000005 00000005 00200046
00000002 00000000 c1082a93 f56c7e28 c2472da8 c1082a93 f5e5fee4 c106bc61^M
00000000 c1082a93 00000000 00000000 00000001 00200046 00200082 00000000
Call Trace:
[<c10687a8>] ftrace_raw_event_lock+0x39/0xc0
[<c1082a93>] ? ktime_get+0x29/0x69
[<c1082a93>] ? ktime_get+0x29/0x69
[<c106bc61>] lock_release+0x57/0x1a5
[<c1082a93>] ? ktime_get+0x29/0x69
[<c10824dd>] read_seqcount_begin.constprop.7+0x4d/0x75
[<c1082a93>] ? ktime_get+0x29/0x69^M
[<c1082a93>] ktime_get+0x29/0x69
[<c108a46a>] __tick_nohz_idle_enter+0x1e/0x426
[<c10690e8>] ? lock_release_holdtime.part.19+0x48/0x4d
[<c10bc184>] ? time_hardirqs_off+0xe/0x28
[<c1068c82>] ? trace_hardirqs_off_caller+0x3f/0xaf
[<c108a8cb>] tick_nohz_idle_enter+0x59/0x62
[<c1079242>] cpu_startup_entry+0x64/0x192
[<c102299c>] start_secondary+0x277/0x27c
Code: 90 89 c6 89 d0 88 c4 ac 38 e0 74 09 84 c0 75 f7 be 01 00 00 00 89 f0 48 5e 5d c3 55 89 e5 57 66 66 66 66 90 83 c9 ff 89 c7 31 c0 <f2> ae f7 d1 8d 41 ff 5f 5d c3 55 89 e5 57 66 66 66 66 90 31 ff
EIP: [<c127a17b>] strlen+0x10/0x1a SS:ESP 0068:f5e5fe80
CR2: 0000000000000000
---[ end trace 01bc47bf519ec1b2 ]---

New tracepoints have been added that have allowed for NULL pointers
being assigned to strings. To fix this, change the TRACE_EVENT() code
to check for NULL and if it is, it will assign "(null)" to it instead
(similar to what glibc printf does).

Reported-by: Shuah Khan <shuah.kh@samsung.com>
Reported-by: Jovi Zhangwei <jovi.zhangwei@gmail.com>
Link: http://lkml.kernel.org/r/CAGdX0WFeEuy+DtpsJzyzn0343qEEjLX97+o1VREFkUEhndC+5Q@mail.gmail.com
Link: http://lkml.kernel.org/r/528D6972.9010702@samsung.com
Fixes: 9cbf117662e2 ("tracing/events: provide string with undefined size support")
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
include/trace/ftrace.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -379,7 +379,8 @@ ftrace_define_fields_##call(struct ftrac
__data_size += (len) * sizeof(type);

#undef __string
-#define __string(item, src) __dynamic_array(char, item, strlen(src) + 1)
+#define __string(item, src) __dynamic_array(char, item, \
+ strlen((src) ? (const char *)(src) : "(null)") + 1)

#undef DECLARE_EVENT_CLASS
#define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print) \
@@ -504,7 +505,7 @@ static inline notrace int ftrace_get_off

#undef __assign_str
#define __assign_str(dst, src) \
- strcpy(__get_str(dst), src);
+ strcpy(__get_str(dst), (src) ? (const char *)(src) : "(null)");

#undef TP_fast_assign
#define TP_fast_assign(args...) args