kernel/trace/trace_events_synth.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-)
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
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
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
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