[PATCH] ftrace: Avoid double-free of dyn_ftrace

[PATCH] ftrace: Avoid double-free of dyn_ftrace

[Zhaolei]

If dyn_ftrace is free before ftrace_release(),
ftrace_release() will free it again and make ftrace_free_records wrong.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
---
 kernel/trace/ftrace.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index d33d306..26c45aa 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -356,7 +356,8 @@ void ftrace_release(void *start, unsigned long size)
 
 	mutex_lock(&ftrace_lock);
 	do_for_each_ftrace_rec(pg, rec) {
-		if ((rec->ip >= s) && (rec->ip < e))
+		if ((rec->ip >= s) && (rec->ip < e) &&
+		    !(rec->flags & FTRACE_FL_FREE))
 			ftrace_free_rec(rec);
 	} while_for_each_ftrace_rec();
 	mutex_unlock(&ftrace_lock);
-- 
1.5.5.3

Re: [PATCH] ftrace: Avoid double-free of dyn_ftrace

[Ingo Molnar]

* Zhaolei <zhaolei@cn.fujitsu.com> wrote:

> If dyn_ftrace is free before ftrace_release(), 
> ftrace_release() will free it again and make 
> ftrace_free_records wrong.
> 
> Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
> ---
>  kernel/trace/ftrace.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index d33d306..26c45aa 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -356,7 +356,8 @@ void ftrace_release(void *start, unsigned long size)
>  
>  	mutex_lock(&ftrace_lock);
>  	do_for_each_ftrace_rec(pg, rec) {
> -		if ((rec->ip >= s) && (rec->ip < e))
> +		if ((rec->ip >= s) && (rec->ip < e) &&
> +		    !(rec->flags & FTRACE_FL_FREE))
>  			ftrace_free_rec(rec);

Applied to tip:tracing/ftrace, thanks!

I'm wondering, did you trigger this in practice (if yes, how?), 
or have you found it via code review?

	Ingo

Re: [PATCH] ftrace: Avoid double-free of dyn_ftrace

[Zhaolei]

* From: "Ingo Molnar" <mingo@elte.hu>
> 
> * Zhaolei <zhaolei@cn.fujitsu.com> wrote:
> 
>> If dyn_ftrace is free before ftrace_release(), 
>> ftrace_release() will free it again and make 
>> ftrace_free_records wrong.
>> 
>> Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
>> ---
>>  kernel/trace/ftrace.c |    3 ++-
>>  1 files changed, 2 insertions(+), 1 deletions(-)
>> 
>> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
>> index d33d306..26c45aa 100644
>> --- a/kernel/trace/ftrace.c
>> +++ b/kernel/trace/ftrace.c
>> @@ -356,7 +356,8 @@ void ftrace_release(void *start, unsigned long size)
>>  
>>  mutex_lock(&ftrace_lock);
>>  do_for_each_ftrace_rec(pg, rec) {
>> - if ((rec->ip >= s) && (rec->ip < e))
>> + if ((rec->ip >= s) && (rec->ip < e) &&
>> +     !(rec->flags & FTRACE_FL_FREE))
>>  ftrace_free_rec(rec);
> 
> Applied to tip:tracing/ftrace, thanks!
> 
> I'm wondering, did you trigger this in practice (if yes, how?), 
> or have you found it via code review?
Hello, Ingo

It is found via code review.

B.R.
Zhaolei
> 
> Ingo
> 
>ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥

[tip:tracing/ftrace] ftrace: avoid double-free of dyn_ftrace

[Zhaolei]

Commit-ID:  b00f0b6dc1773b4c8f538503247da050b5ea631b
Gitweb:     http://git.kernel.org/tip/b00f0b6dc1773b4c8f538503247da050b5ea631b
Author:     Zhaolei <zhaolei@cn.fujitsu.com>
AuthorDate: Fri, 13 Mar 2009 17:14:01 +0800
Commit:     Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 13 Mar 2009 10:25:06 +0100

ftrace: avoid double-free of dyn_ftrace

If dyn_ftrace is freed before ftrace_release(), ftrace_release()
will free it again and make ftrace_free_records wrong.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Cc: "Steven Rostedt ;" <rostedt@goodmis.org>
LKML-Reference: <49BA23D9.1050900@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
 kernel/trace/ftrace.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index d33d306..26c45aa 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -356,7 +356,8 @@ void ftrace_release(void *start, unsigned long size)
 
 	mutex_lock(&ftrace_lock);
 	do_for_each_ftrace_rec(pg, rec) {
-		if ((rec->ip >= s) && (rec->ip < e))
+		if ((rec->ip >= s) && (rec->ip < e) &&
+		    !(rec->flags & FTRACE_FL_FREE))
 			ftrace_free_rec(rec);
 	} while_for_each_ftrace_rec();
 	mutex_unlock(&ftrace_lock);

Re: [PATCH] ftrace: Avoid double-free of dyn_ftrace

[Steven Rostedt]

On Fri, 13 Mar 2009, Zhaolei wrote:

> * From: "Ingo Molnar" <mingo@elte.hu>
> > 
> > * Zhaolei <zhaolei@cn.fujitsu.com> wrote:
> > 
> >> If dyn_ftrace is free before ftrace_release(), 
> >> ftrace_release() will free it again and make 
> >> ftrace_free_records wrong.
> >> 
> >> Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
> >> ---
> >>  kernel/trace/ftrace.c |    3 ++-
> >>  1 files changed, 2 insertions(+), 1 deletions(-)
> >> 
> >> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> >> index d33d306..26c45aa 100644
> >> --- a/kernel/trace/ftrace.c
> >> +++ b/kernel/trace/ftrace.c
> >> @@ -356,7 +356,8 @@ void ftrace_release(void *start, unsigned long size)
> >>  
> >>  mutex_lock(&ftrace_lock);
> >>  do_for_each_ftrace_rec(pg, rec) {
> >> - if ((rec->ip >= s) && (rec->ip < e))
> >> + if ((rec->ip >= s) && (rec->ip < e) &&
> >> +     !(rec->flags & FTRACE_FL_FREE))
> >>  ftrace_free_rec(rec);
> > 
> > Applied to tip:tracing/ftrace, thanks!
> > 
> > I'm wondering, did you trigger this in practice (if yes, how?), 
> > or have you found it via code review?
> Hello, Ingo
> 
> It is found via code review.

Hmm, could you explain this more. I'm thinking that this scenario should 
not happen, and if it does, it should probably be a bug.

Because when we call ftrace_free_rec we change the rec->ip to point to the 
next record in the chain. Something is very wrong if rec->ip >= s && 
rec->ip < e and the record is already free.

We can add a:

	WARN_ON(rec->flags & FTRACE_FL_FREE);

in ftrace_free_rec if you are worried about this happening.

-- Steve

Re: [PATCH] ftrace: Avoid double-free of dyn_ftrace

[Zhaolei]

* From: "Steven Rostedt" <rostedt@goodmis.org>
> On Fri, 13 Mar 2009, Zhaolei wrote:
> 
>> * From: "Ingo Molnar" <mingo@elte.hu>
>> > 
>> > * Zhaolei <zhaolei@cn.fujitsu.com> wrote:
>> > 
>> >> If dyn_ftrace is free before ftrace_release(), 
>> >> ftrace_release() will free it again and make 
>> >> ftrace_free_records wrong.
>> >> 
>> >> Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
>> >> ---
>> >>  kernel/trace/ftrace.c |    3 ++-
>> >>  1 files changed, 2 insertions(+), 1 deletions(-)
>> >> 
>> >> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
>> >> index d33d306..26c45aa 100644
>> >> --- a/kernel/trace/ftrace.c
>> >> +++ b/kernel/trace/ftrace.c
>> >> @@ -356,7 +356,8 @@ void ftrace_release(void *start, unsigned long size)
>> >>  
>> >>  mutex_lock(&ftrace_lock);
>> >>  do_for_each_ftrace_rec(pg, rec) {
>> >> - if ((rec->ip >= s) && (rec->ip < e))
>> >> + if ((rec->ip >= s) && (rec->ip < e) &&
>> >> +     !(rec->flags & FTRACE_FL_FREE))
>> >>  ftrace_free_rec(rec);
>> > 
>> > Applied to tip:tracing/ftrace, thanks!
>> > 
>> > I'm wondering, did you trigger this in practice (if yes, how?), 
>> > or have you found it via code review?
>> Hello, Ingo
>> 
>> It is found via code review.
> 
> Hmm, could you explain this more. I'm thinking that this scenario should 
> not happen, and if it does, it should probably be a bug.
> 
> Because when we call ftrace_free_rec we change the rec->ip to point to the 
> next record in the chain. Something is very wrong if rec->ip >= s && 
> rec->ip < e and the record is already free.
Hello, Steven

Thanks for your comment.
I got your meaning, and I agree that if rec->ip >= s && rec->ip < e,
this record is not freed.
But IMHO, "if rec->ip >= s && rec->ip < e" is used to select records in the module,
and function of ignore "freed record" is only its side-effect.
So, add a special judgement to avoid "freed record" is not a bad idea.
And I also agree your suggestion of add a WARN_ON, because this should not happened.

B.R.
Zhaolei

> 
> We can add a:
> 
> WARN_ON(rec->flags & FTRACE_FL_FREE);
> 
> in ftrace_free_rec if you are worried about this happening.
> 
> -- Steve
> 
> 
>ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥

Re: [PATCH] ftrace: Avoid double-free of dyn_ftrace

[Steven Rostedt]

On Wed, Mar 25, 2009 at 10:25:47AM +0800, Zhaolei wrote:
> >> > 
> >> > I'm wondering, did you trigger this in practice (if yes, how?), 
> >> > or have you found it via code review?
> >> Hello, Ingo
> >> 
> >> It is found via code review.
> > 
> > Hmm, could you explain this more. I'm thinking that this scenario should 
> > not happen, and if it does, it should probably be a bug.
> > 
> > Because when we call ftrace_free_rec we change the rec->ip to point to the 
> > next record in the chain. Something is very wrong if rec->ip >= s && 
> > rec->ip < e and the record is already free.
> Hello, Steven
> 
> Thanks for your comment.
> I got your meaning, and I agree that if rec->ip >= s && rec->ip < e,
> this record is not freed.
> But IMHO, "if rec->ip >= s && rec->ip < e" is used to select records in the module,
> and function of ignore "freed record" is only its side-effect.
> So, add a special judgement to avoid "freed record" is not a bad idea.
> And I also agree your suggestion of add a WARN_ON, because this should not happened.

Hi Zhaolei,

Great! Feel free to send another patch ;-)

Note, use FTRACE_WARN_ON() macro. This way it shuts down ftrace if it is hit and 
helps to avoid further damage later.

-- Steve