Re: [PATCH] tracing/probe: Fix to check the difference of nr_args before adding probe

[Steven Rostedt <rostedt@goodmis.org>]

On Sat, 28 Sep 2019 02:59:08 -0700
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Fix to check the difference of nr_args before adding probe
> on existing probes. This also may set the error log index
> bigger than the number of command parameters. In that case
> it sets the error position is next to the last parameter.
> 
> Fixes: ca89bc071d5e ("tracing/kprobe: Add multi-probe per event support")
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>

I modified the change log a bit, below is the patch I plan on submitting.

You OK with this?

-- Steve


From: Masami Hiramatsu <mhiramat@kernel.org>
Date: Sat, 28 Sep 2019 05:53:29 -0400
Subject: [PATCH] tracing/probe: Fix to check the difference of nr_args before
 adding probe

Steven reported that a test triggered:

==================================================================
 BUG: KASAN: slab-out-of-bounds in trace_kprobe_create+0xa9e/0xe40
 Read of size 8 at addr ffff8880c4f25a48 by task ftracetest/4798

 CPU: 2 PID: 4798 Comm: ftracetest Not tainted 5.3.0-rc6-test+ #30
 Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01 v03.03 07/14/2016
 Call Trace:
  dump_stack+0x7c/0xc0
  ? trace_kprobe_create+0xa9e/0xe40
  print_address_description+0x6c/0x332
  ? trace_kprobe_create+0xa9e/0xe40
  ? trace_kprobe_create+0xa9e/0xe40
  __kasan_report.cold.6+0x1a/0x3b
  ? trace_kprobe_create+0xa9e/0xe40
  kasan_report+0xe/0x12
  trace_kprobe_create+0xa9e/0xe40
  ? print_kprobe_event+0x280/0x280
  ? match_held_lock+0x1b/0x240
  ? find_held_lock+0xac/0xd0
  ? fs_reclaim_release.part.112+0x5/0x20
  ? lock_downgrade+0x350/0x350
  ? kasan_unpoison_shadow+0x30/0x40
  ? __kasan_kmalloc.constprop.6+0xc1/0xd0
  ? trace_kprobe_create+0xe40/0xe40
  ? trace_kprobe_create+0xe40/0xe40
  create_or_delete_trace_kprobe+0x2e/0x60
  trace_run_command+0xc3/0xe0
  ? trace_panic_handler+0x20/0x20
  ? kasan_unpoison_shadow+0x30/0x40
  trace_parse_run_command+0xdc/0x163
  vfs_write+0xe1/0x240
  ksys_write+0xba/0x150
  ? __ia32_sys_read+0x50/0x50
  ? tracer_hardirqs_on+0x61/0x180
  ? trace_hardirqs_off_caller+0x43/0x110
  ? mark_held_locks+0x29/0xa0
  ? do_syscall_64+0x14/0x260
  do_syscall_64+0x68/0x260

Fix to check the difference of nr_args before adding probe
on existing probes. This also may set the error log index
bigger than the number of command parameters. In that case
it sets the error position is next to the last parameter.

Link: http://lkml.kernel.org/r/156966474783.3478.13217501608215769150.stgit@devnote2

Fixes: ca89bc071d5e ("tracing/kprobe: Add multi-probe per event support")
Reported-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel/trace/trace_probe.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index baf58a3612c0..905b10af5d5c 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -178,6 +178,16 @@ void __trace_probe_log_err(int offset, int err_type)
 	if (!command)
 		return;
 
+	if (trace_probe_log.index >= trace_probe_log.argc) {
+		/**
+		 * Set the error position is next to the last arg + space.
+		 * Note that len includes the terminal null and the cursor
+		 * appaers at pos + 1.
+		 */
+		pos = len;
+		offset = 0;
+	}
+
 	/* And make a command string from argv array */
 	p = command;
 	for (i = 0; i < trace_probe_log.argc; i++) {
@@ -1084,6 +1094,12 @@ int trace_probe_compare_arg_type(struct trace_probe *a, struct trace_probe *b)
 {
 	int i;
 
+	/* In case of more arguments */
+	if (a->nr_args < b->nr_args)
+		return a->nr_args + 1;
+	if (a->nr_args > b->nr_args)
+		return b->nr_args + 1;
+
 	for (i = 0; i < a->nr_args; i++) {
 		if ((b->nr_args <= i) ||
 		    ((a->args[i].type != b->args[i].type) ||
-- 
2.20.1