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Message-Id: <20250512092442.32527a9e0dca2aeabcd07bf3@kernel.org>
Date: Mon, 12 May 2025 09:24:42 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, Paul Cacheux
<paulcacheux@...il.com>, Mathieu Desnoyers
<mathieu.desnoyers@...icios.com>, Namhyung Kim <namhyung@...nel.org>,
linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: probes: Fix a possible race in trace_probe_log
APIs
On Sat, 10 May 2025 12:44:41 +0900
"Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:
> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
>
> Since the shared trace_probe_log variable can be accessed and
> modified via probe event create operation of kprobe_events,
> uprobe_events, and dynamic_events, it should be protected.
> In the dynamic_events, all operations are serialized by
> `dyn_event_ops_mutex`. But kprobe_events and uprobe_events
> interfaces are not serialized.
>
> To solve this issue, introduces dyn_event_create(), which runs
> create() operation under the mutex, for kprobe_events and
> uprobe_events. This also uses lockdep to check the mutex is
> held when using trace_probe_log* APIs.
>
> Reported-by: Paul Cacheux <paulcacheux@...il.com>
> Closes: https://lore.kernel.org/all/20250510074456.805a16872b591e2971a4d221@kernel.org/
BTW, this fixes the problem introduced by commit ab105a4fb894
("tracing: Use tracing error_log with probe events"). However,
this patch can be applied after commit d262271d0483
("tracing/dynevent: Delegate parsing to create function").
Thus, before that commit, we may need another way to fix
this issue. (e.g. introduce a different mutex.)
Anyway, to record the correct fixes;
Fixes: ab105a4fb894 ("tracing: Use tracing error_log with probe events")
Thanks,
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> ---
> kernel/trace/trace_dynevent.c | 16 +++++++++++++++-
> kernel/trace/trace_dynevent.h | 1 +
> kernel/trace/trace_kprobe.c | 2 +-
> kernel/trace/trace_probe.c | 9 +++++++++
> kernel/trace/trace_uprobe.c | 2 +-
> 5 files changed, 27 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/trace/trace_dynevent.c b/kernel/trace/trace_dynevent.c
> index a322e4f249a5..5d64a18cacac 100644
> --- a/kernel/trace/trace_dynevent.c
> +++ b/kernel/trace/trace_dynevent.c
> @@ -16,7 +16,7 @@
> #include "trace_output.h" /* for trace_event_sem */
> #include "trace_dynevent.h"
>
> -static DEFINE_MUTEX(dyn_event_ops_mutex);
> +DEFINE_MUTEX(dyn_event_ops_mutex);
> static LIST_HEAD(dyn_event_ops_list);
>
> bool trace_event_dyn_try_get_ref(struct trace_event_call *dyn_call)
> @@ -116,6 +116,20 @@ int dyn_event_release(const char *raw_command, struct dyn_event_operations *type
> return ret;
> }
>
> +/*
> + * Locked version of event creation. The event creation must be protected by
> + * dyn_event_ops_mutex because of protecting trace_probe_log.
> + */
> +int dyn_event_create(const char *raw_command, struct dyn_event_operations *type)
> +{
> + int ret;
> +
> + mutex_lock(&dyn_event_ops_mutex);
> + ret = type->create(raw_command);
> + mutex_unlock(&dyn_event_ops_mutex);
> + return ret;
> +}
> +
> static int create_dyn_event(const char *raw_command)
> {
> struct dyn_event_operations *ops;
> diff --git a/kernel/trace/trace_dynevent.h b/kernel/trace/trace_dynevent.h
> index 936477a111d3..beee3f8d7544 100644
> --- a/kernel/trace/trace_dynevent.h
> +++ b/kernel/trace/trace_dynevent.h
> @@ -100,6 +100,7 @@ void *dyn_event_seq_next(struct seq_file *m, void *v, loff_t *pos);
> void dyn_event_seq_stop(struct seq_file *m, void *v);
> int dyn_events_release_all(struct dyn_event_operations *type);
> int dyn_event_release(const char *raw_command, struct dyn_event_operations *type);
> +int dyn_event_create(const char *raw_command, struct dyn_event_operations *type);
>
> /*
> * for_each_dyn_event - iterate over the dyn_event list
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 2703b96d8990..3e5c47b6d7b2 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1089,7 +1089,7 @@ static int create_or_delete_trace_kprobe(const char *raw_command)
> if (raw_command[0] == '-')
> return dyn_event_release(raw_command, &trace_kprobe_ops);
>
> - ret = trace_kprobe_create(raw_command);
> + ret = dyn_event_create(raw_command, &trace_kprobe_ops);
> return ret == -ECANCELED ? -EINVAL : ret;
> }
>
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index 2eeecb6c95ee..424751cdf31f 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -154,9 +154,12 @@ static const struct fetch_type *find_fetch_type(const char *type, unsigned long
> }
>
> static struct trace_probe_log trace_probe_log;
> +extern struct mutex dyn_event_ops_mutex;
>
> void trace_probe_log_init(const char *subsystem, int argc, const char **argv)
> {
> + lockdep_assert_held(&dyn_event_ops_mutex);
> +
> trace_probe_log.subsystem = subsystem;
> trace_probe_log.argc = argc;
> trace_probe_log.argv = argv;
> @@ -165,11 +168,15 @@ void trace_probe_log_init(const char *subsystem, int argc, const char **argv)
>
> void trace_probe_log_clear(void)
> {
> + lockdep_assert_held(&dyn_event_ops_mutex);
> +
> memset(&trace_probe_log, 0, sizeof(trace_probe_log));
> }
>
> void trace_probe_log_set_index(int index)
> {
> + lockdep_assert_held(&dyn_event_ops_mutex);
> +
> trace_probe_log.index = index;
> }
>
> @@ -178,6 +185,8 @@ void __trace_probe_log_err(int offset, int err_type)
> char *command, *p;
> int i, len = 0, pos = 0;
>
> + lockdep_assert_held(&dyn_event_ops_mutex);
> +
> if (!trace_probe_log.argv)
> return;
>
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 3386439ec9f6..35cf76c75dd7 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -741,7 +741,7 @@ static int create_or_delete_trace_uprobe(const char *raw_command)
> if (raw_command[0] == '-')
> return dyn_event_release(raw_command, &trace_uprobe_ops);
>
> - ret = trace_uprobe_create(raw_command);
> + ret = dyn_event_create(raw_command, &trace_uprobe_ops);
> return ret == -ECANCELED ? -EINVAL : ret;
> }
>
>
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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