linux-kernel - Re: [BUGFIX PATCH] tracing/kprobes: Fix strpbrk() argument order

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Date:   Fri, 2 Nov 2018 09:54:24 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [BUGFIX PATCH] tracing/kprobes: Fix strpbrk() argument order

On Fri, 2 Nov 2018 16:14:59 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Thu, 1 Nov 2018 15:10:14 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > On Thu,  1 Nov 2018 23:29:28 +0900
> > Masami Hiramatsu <mhiramat@...nel.org> wrote:
> >   
> > > Fix strpbrk()'s argument order, it must pass acceptable string
> > > in 2nd argument. Note that this can cause a kernel panic where
> > > it recovers backup character to code->data.
> > > 
> > > Fixes: a6682814f371 ("tracing/kprobes: Allow kprobe-events to record module symbol")
> > > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>  
> > 
> > Thanks Masami,
> > 
> > I'm pulling this and starting to test it.  
> 
> Thank you! I still couldn't believe how this bug passed through the tests...

I am too. I'm running tests with and without this patch, and the patch
doesn't appear to be making much difference.

Then I tested with this:

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 3ef15a6683c0..4ddafddf1343 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -516,6 +516,7 @@ void traceprobe_free_probe_arg(struct probe_arg
*arg) kfree(code->data);
 		code++;
 	}
+	printk("free arg->code %s\n", arg->code);
 	kfree(arg->code);
 	kfree(arg->name);
 	kfree(arg->comm);
@@ -535,11 +536,15 @@ int traceprobe_update_arg(struct probe_arg *arg)
 			if (code[1].op != FETCH_OP_IMM)
 				return -EINVAL;
 
+			tmp = strpbrk(code->data, "+-");
+			printk("first tmp tmp=%s\n", tmp);
 			tmp = strpbrk("+-", code->data);
+			printk("second tmp=%s data=%s\n", tmp,
code->data); if (tmp)
 				c = *tmp;
 			ret =
traceprobe_split_symbol_offset(code->data, &offset);
+			printk("third data=%s\n", code->data);
 			if (ret)
 				return ret;
 
@@ -547,6 +552,7 @@ int traceprobe_update_arg(struct probe_arg *arg)
 				(unsigned
long)kallsyms_lookup_name(code->data); if (tmp)
 				*tmp = c;
+			printk("forth data=%s\n", code->data);
 			if (!code[1].immediate)
 				return -ENOENT;
 			code[1].immediate += offset;

And I don't see where that code->data is used elsewhere. That is, why
even bother saving the character?

-- Steve