* [PATCH] tracing: Fix use-after-free and double-free on last_cmd
@ 2023-03-17 5:30 Cheng-Jui Wang
2023-03-18 18:35 ` Steven Rostedt
0 siblings, 1 reply; 3+ messages in thread
From: Cheng-Jui Wang @ 2023-03-17 5:30 UTC (permalink / raw)
To: Steven Rostedt, Masami Hiramatsu, Matthias Brugger,
AngeloGioacchino Del Regno, Tom Zanussi
Cc: Bobule.chang, wsd_upstream, Tze-nan Wu, stable, linux-kernel,
linux-trace-kernel, linux-arm-kernel, linux-mediatek
From: "Tze-nan Wu" <Tze-nan.Wu@mediatek.com>
Currently, the last_cmd variable can be accessed by multiple processes
asynchronously when multiple users manipulate synthetic_events node
at the same time, it could lead to use-after-free or double-free.
This patch add lastcmd_mutex to prevent last_cmd from being accessed
asynchronously.
================================================================
It's easy to reproduce in the KASAN environment by running the two
scripts below in different shells.
script 1:
while :
do
echo -n -e '\x88' > /sys/kernel/tracing/synthetic_events
done
script 2:
while :
do
echo -n -e '\xb0' > /sys/kernel/tracing/synthetic_events
done
================================================================
double-free scenario:
process A process B
------------------- ---------------
1.kstrdup last_cmd
2.free last_cmd
3.free last_cmd(double-free)
================================================================
use-after-free scenario:
process A process B
------------------- ---------------
1.kstrdup last_cmd
2.free last_cmd
3.tracing_log_err(use-after-free)
================================================================
Appendix 1. KASAN report double-free:
BUG: KASAN: double-free in kfree+0xdc/0x1d4
Free of addr ***** by task sh/4879
Call trace:
...
kfree+0xdc/0x1d4
create_or_delete_synth_event+0x60/0x1e8
trace_parse_run_command+0x2bc/0x4b8
synth_events_write+0x20/0x30
vfs_write+0x200/0x830
...
Allocated by task 4879:
...
kstrdup+0x5c/0x98
create_or_delete_synth_event+0x6c/0x1e8
trace_parse_run_command+0x2bc/0x4b8
synth_events_write+0x20/0x30
vfs_write+0x200/0x830
...
Freed by task 5464:
...
kfree+0xdc/0x1d4
create_or_delete_synth_event+0x60/0x1e8
trace_parse_run_command+0x2bc/0x4b8
synth_events_write+0x20/0x30
vfs_write+0x200/0x830
...
================================================================
Appendix 2. KASAN report use-after-free:
BUG: KASAN: use-after-free in strlen+0x5c/0x7c
Read of size 1 at addr ***** by task sh/5483
sh: CPU: 7 PID: 5483 Comm: sh
...
__asan_report_load1_noabort+0x34/0x44
strlen+0x5c/0x7c
tracing_log_err+0x60/0x444
create_or_delete_synth_event+0xc4/0x204
trace_parse_run_command+0x2bc/0x4b8
synth_events_write+0x20/0x30
vfs_write+0x200/0x830
...
Allocated by task 5483:
...
kstrdup+0x5c/0x98
create_or_delete_synth_event+0x80/0x204
trace_parse_run_command+0x2bc/0x4b8
synth_events_write+0x20/0x30
vfs_write+0x200/0x830
...
Freed by task 5480:
...
kfree+0xdc/0x1d4
create_or_delete_synth_event+0x74/0x204
trace_parse_run_command+0x2bc/0x4b8
synth_events_write+0x20/0x30
vfs_write+0x200/0x830
...
Fixes: 27c888da9867 ("tracing: Remove size restriction on synthetic event cmd error logging")
Cc: stable@vger.kernel.org
Signed-off-by: Tze-nan Wu <Tze-nan.Wu@mediatek.com>
---
kernel/trace/trace_events_synth.c | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index 46d0abb32d0f..ce438eccab2e 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -42,16 +42,25 @@ enum { ERRORS };
#undef C
#define C(a, b) b
+static DEFINE_MUTEX(lastcmd_mutex);
+
static const char *err_text[] = { ERRORS };
static char *last_cmd;
static int errpos(const char *str)
{
- if (!str || !last_cmd)
- return 0;
+ int ret = 0;
+
+ mutex_lock(&lastcmd_mutex);
+ if (!str || !last_cmd) {
+ mutex_unlock(&lastcmd_mutex);
+ return ret;
+ }
- return err_pos(last_cmd, str);
+ ret = err_pos(last_cmd, str);
+ mutex_unlock(&lastcmd_mutex);
+ return ret;
}
static void last_cmd_set(const char *str)
@@ -59,18 +68,24 @@ static void last_cmd_set(const char *str)
if (!str)
return;
+ mutex_lock(&lastcmd_mutex);
kfree(last_cmd);
last_cmd = kstrdup(str, GFP_KERNEL);
+ mutex_unlock(&lastcmd_mutex);
}
static void synth_err(u8 err_type, u16 err_pos)
{
- if (!last_cmd)
+ mutex_lock(&lastcmd_mutex);
+ if (!last_cmd) {
+ mutex_unlock(&lastcmd_mutex);
return;
+ }
tracing_log_err(NULL, "synthetic_events", last_cmd, err_text,
err_type, err_pos);
+ mutex_unlock(&lastcmd_mutex);
}
static int create_synth_event(const char *raw_command);
--
2.18.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] tracing: Fix use-after-free and double-free on last_cmd
2023-03-17 5:30 [PATCH] tracing: Fix use-after-free and double-free on last_cmd Cheng-Jui Wang
@ 2023-03-18 18:35 ` Steven Rostedt
2023-03-21 11:23 ` Tze-nan Wu (吳澤南)
0 siblings, 1 reply; 3+ messages in thread
From: Steven Rostedt @ 2023-03-18 18:35 UTC (permalink / raw)
To: Cheng-Jui Wang
Cc: Masami Hiramatsu, Matthias Brugger, AngeloGioacchino Del Regno,
Tom Zanussi, Bobule.chang, wsd_upstream, Tze-nan Wu, stable,
linux-kernel, linux-trace-kernel, linux-arm-kernel,
linux-mediatek
On Fri, 17 Mar 2023 13:30:44 +0800
Cheng-Jui Wang <cheng-jui.wang@mediatek.com> wrote:
> From: "Tze-nan Wu" <Tze-nan.Wu@mediatek.com>
Hi!
Thanks for the report and the patch. Some nits below.
Also change the subject to:
tracing/synthetic: Fix races on freeing last_cmd
> ---
> kernel/trace/trace_events_synth.c | 23 +++++++++++++++++++----
> 1 file changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
> index 46d0abb32d0f..ce438eccab2e 100644
> --- a/kernel/trace/trace_events_synth.c
> +++ b/kernel/trace/trace_events_synth.c
> @@ -42,16 +42,25 @@ enum { ERRORS };
> #undef C
> #define C(a, b) b
>
> +static DEFINE_MUTEX(lastcmd_mutex);
> +
> static const char *err_text[] = { ERRORS };
>
> static char *last_cmd;
Please keep the mutex and the variable it protects next to each other:
static DEFINE_MUTEX(lastcmd_mutex);
static char *last_cmd;
>
> static int errpos(const char *str)
> {
> - if (!str || !last_cmd)
> - return 0;
> + int ret = 0;
> +
> + mutex_lock(&lastcmd_mutex);
> + if (!str || !last_cmd) {
Change this to just:
if (!str || !last_cmd)
goto out;
> + mutex_unlock(&lastcmd_mutex);
> + return ret;
> + }
>
> - return err_pos(last_cmd, str);
> + ret = err_pos(last_cmd, str);
Add:
out:
> + mutex_unlock(&lastcmd_mutex);
> + return ret;
> }
>
> static void last_cmd_set(const char *str)
> @@ -59,18 +68,24 @@ static void last_cmd_set(const char *str)
> if (!str)
> return;
>
> + mutex_lock(&lastcmd_mutex);
> kfree(last_cmd);
>
In this case, you can remove the space:
mutex_lock(&lastcmd_mutex);
kfree(last_cmd);
last_cmd = kstrdup(str, GFP_KERNEL);
mutex_unlock(&lastcmd_mutex);
> last_cmd = kstrdup(str, GFP_KERNEL);
> + mutex_unlock(&lastcmd_mutex);
> }
>
> static void synth_err(u8 err_type, u16 err_pos)
> {
> - if (!last_cmd)
> + mutex_lock(&lastcmd_mutex);
> + if (!last_cmd) {
This should be:
if (!last_cmd)
goto out;
> + mutex_unlock(&lastcmd_mutex);
> return;
> + }
>
> tracing_log_err(NULL, "synthetic_events", last_cmd, err_text,
> err_type, err_pos);
out:
> + mutex_unlock(&lastcmd_mutex);
> }
>
> static int create_synth_event(const char *raw_command);
Thanks,
-- Steve
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] tracing: Fix use-after-free and double-free on last_cmd
2023-03-18 18:35 ` Steven Rostedt
@ 2023-03-21 11:23 ` Tze-nan Wu (吳澤南)
0 siblings, 0 replies; 3+ messages in thread
From: Tze-nan Wu (吳澤南) @ 2023-03-21 11:23 UTC (permalink / raw)
To: Cheng-Jui Wang (王正睿), rostedt
Cc: zanussi, linux-kernel, linux-trace-kernel, linux-mediatek,
wsd_upstream, Bobule Chang (張弘義),
stable, linux-arm-kernel, mhiramat, matthias.bgg,
angelogioacchino.delregno
On Sat, 2023-03-18 at 14:35 -0400, Steven Rostedt wrote:
> On Fri, 17 Mar 2023 13:30:44 +0800
> Cheng-Jui Wang <cheng-jui.wang@mediatek.com> wrote:
>
> > From: "Tze-nan Wu" <Tze-nan.Wu@mediatek.com>
>
> Hi!
>
> Thanks for the report and the patch. Some nits below.
>
> Also change the subject to:
>
> tracing/synthetic: Fix races on freeing last_cmd
>
> > ---
> > kernel/trace/trace_events_synth.c | 23 +++++++++++++++++++----
> > 1 file changed, 19 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/trace/trace_events_synth.c
> > b/kernel/trace/trace_events_synth.c
> > index 46d0abb32d0f..ce438eccab2e 100644
> > --- a/kernel/trace/trace_events_synth.c
> > +++ b/kernel/trace/trace_events_synth.c
> > @@ -42,16 +42,25 @@ enum { ERRORS };
> > #undef C
> > #define C(a, b) b
> >
> > +static DEFINE_MUTEX(lastcmd_mutex);
> > +
> > static const char *err_text[] = { ERRORS };
> >
> > static char *last_cmd;
>
> Please keep the mutex and the variable it protects next to each
> other:
>
> static DEFINE_MUTEX(lastcmd_mutex);
> static char *last_cmd;
>
> >
> > static int errpos(const char *str)
> > {
> > - if (!str || !last_cmd)
> > - return 0;
> > + int ret = 0;
> > +
> > + mutex_lock(&lastcmd_mutex);
> > + if (!str || !last_cmd) {
>
> Change this to just:
>
> if (!str || !last_cmd)
> goto out;
>
> > + mutex_unlock(&lastcmd_mutex);
> > + return ret;
> > + }
> >
> > - return err_pos(last_cmd, str);
> > + ret = err_pos(last_cmd, str);
>
> Add:
>
> out:
>
> > + mutex_unlock(&lastcmd_mutex);
> > + return ret;
> > }
> >
> > static void last_cmd_set(const char *str)
> > @@ -59,18 +68,24 @@ static void last_cmd_set(const char *str)
> > if (!str)
> > return;
> >
> > + mutex_lock(&lastcmd_mutex);
> > kfree(last_cmd);
> >
>
> In this case, you can remove the space:
>
> mutex_lock(&lastcmd_mutex);
> kfree(last_cmd);
> last_cmd = kstrdup(str, GFP_KERNEL);
> mutex_unlock(&lastcmd_mutex);
>
> > last_cmd = kstrdup(str, GFP_KERNEL);
> > + mutex_unlock(&lastcmd_mutex);
> > }
> >
> > static void synth_err(u8 err_type, u16 err_pos)
> > {
> > - if (!last_cmd)
> > + mutex_lock(&lastcmd_mutex);
> > + if (!last_cmd) {
>
> This should be:
>
> if (!last_cmd)
> goto out;
>
> > + mutex_unlock(&lastcmd_mutex);
> > return;
> > + }
> >
> > tracing_log_err(NULL, "synthetic_events", last_cmd, err_text,
> > err_type, err_pos);
>
> out:
>
> > + mutex_unlock(&lastcmd_mutex);
> > }
> >
> > static int create_synth_event(const char *raw_command);
>
> Thanks,
>
> -- Steve
Hi Steve,
Thanks for the comments,
the new patch with cleaner code is now ready.
Since the topic has been changed, I created a new thread for the new
patch:
https://lore.kernel.org/lkml/20230321110444.1587-1-Tze-nan.Wu@mediatek.com/
-- Tze-nan
^ permalink raw reply [flat|nested] 3+ messages in thread
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2023-03-17 5:30 [PATCH] tracing: Fix use-after-free and double-free on last_cmd Cheng-Jui Wang
2023-03-18 18:35 ` Steven Rostedt
2023-03-21 11:23 ` Tze-nan Wu (吳澤南)
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