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Date: Tue, 28 Mar 2017 22:08:41 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Namhyung Kim <namhyung@...nel.org> Cc: Ingo Molnar <mingo@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>, LKML <linux-kernel@...r.kernel.org>, kernel-team@....com Subject: Re: [PATCH 1/4] ftrace: Fix function pid filter on instances On Wed, 29 Mar 2017 10:46:22 +0900 Namhyung Kim <namhyung@...nel.org> wrote: > When function tracer has a pid filter, it adds a probe to sched_switch > to track if current task can be ignored. The probe checks the > ftrace_ignore_pid from current tr to filter tasks. But it misses to > delete the probe when removing an instance so that it can cause a crash > due to the invalid tr pointer (use-after-free). > > This is easily reproducible with the following: > > # cd /sys/kernel/debug/tracing > # mkdir instances/buggy > # echo $$ > instances/buggy/set_ftrace_pid > # rmdir instances/buggy > > ============================================================================ > BUG: KASAN: use-after-free in ftrace_filter_pid_sched_switch_probe+0x3d/0x90 > Read of size 8 by task kworker/0:1/17 > CPU: 0 PID: 17 Comm: kworker/0:1 Tainted: G B 4.11.0-rc3 #198 > Call Trace: > dump_stack+0x68/0x9f > kasan_object_err+0x21/0x70 > kasan_report.part.1+0x22b/0x500 > ? ftrace_filter_pid_sched_switch_probe+0x3d/0x90 > kasan_report+0x25/0x30 > __asan_load8+0x5e/0x70 > ftrace_filter_pid_sched_switch_probe+0x3d/0x90 > ? fpid_start+0x130/0x130 > __schedule+0x571/0xce0 > ... > > To fix it, use ftrace_pid_reset() to unregister the probe. As > instance_rmdir() already updated ftrace codes, it can just free the > filter safely. > > Fixes: 0c8916c34203 ("tracing: Add rmdir to remove multibuffer instances") > Signed-off-by: Namhyung Kim <namhyung@...nel.org> > --- > kernel/trace/ftrace.c | 10 ++++++---- > kernel/trace/trace.c | 1 + > kernel/trace/trace.h | 2 ++ > 3 files changed, 9 insertions(+), 4 deletions(-) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index 0556a202c055..b451a860e885 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -5598,13 +5598,15 @@ static void clear_ftrace_pids(struct trace_array *tr) > trace_free_pid_list(pid_list); > } > > -static void ftrace_pid_reset(struct trace_array *tr) > +void ftrace_pid_reset(struct trace_array *tr, bool update) > { > mutex_lock(&ftrace_lock); > clear_ftrace_pids(tr); > > - ftrace_update_pid_func(); > - ftrace_startup_all(0); > + if (update) { > + ftrace_update_pid_func(); > + ftrace_startup_all(0); > + } > > mutex_unlock(&ftrace_lock); > } I think it is better to create a new function here. I mean, you just added a bool, that removes 2 thirds of the code when false. > @@ -5676,7 +5678,7 @@ ftrace_pid_open(struct inode *inode, struct file *file) > > if ((file->f_mode & FMODE_WRITE) && > (file->f_flags & O_TRUNC)) > - ftrace_pid_reset(tr); > + ftrace_pid_reset(tr, true); > > ret = seq_open(file, &ftrace_pid_sops); > if (ret < 0) { > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index b5d4b80f2d45..b92489dfa829 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -7485,6 +7485,7 @@ static int instance_rmdir(const char *name) > > tracing_set_nop(tr); > event_trace_del_tracer(tr); > + ftrace_pid_reset(tr, false); Actually, if this is called after event_trace_del_tracer(), the tr is already invisible and nothing new should change. Make a wrapper around clear_ftrace_pids() and call that instead. We don't even need to take a lock, but as I see there's a lockdep test for ftrace_lock, we should still do so just to be safe. void ftrace_clear_pids(struct trace_array *tr) { mutex_lock(&ftrace_lock); clear_ftrace_pids(tr); mutex_unlock(&ftrace_lock); } -- Steve > ftrace_destroy_function_files(tr); > tracefs_remove_recursive(tr->dir); > free_trace_buffers(tr); > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h > index 571acee52a32..4d9804fd9a2d 100644 > --- a/kernel/trace/trace.h > +++ b/kernel/trace/trace.h > @@ -897,6 +897,7 @@ void ftrace_init_tracefs(struct trace_array *tr, struct dentry *d_tracer); > void ftrace_init_tracefs_toplevel(struct trace_array *tr, > struct dentry *d_tracer); > int init_function_trace(void); > +void ftrace_pid_reset(struct trace_array *tr, bool update); > #else > static inline int ftrace_trace_task(struct trace_array *tr) > { > @@ -916,6 +917,7 @@ static inline void ftrace_reset_array_ops(struct trace_array *tr) { } > static inline void ftrace_init_tracefs(struct trace_array *tr, struct dentry *d) { } > static inline void ftrace_init_tracefs_toplevel(struct trace_array *tr, struct dentry *d) { } > static inline int init_function_trace(void) { return 0; } > +static inline void ftrace_pid_reset(struct trace_array *tr, bool update) { } > /* ftace_func_t type is not defined, use macro instead of static inline */ > #define ftrace_init_array_ops(tr, func) do { } while (0) > #endif /* CONFIG_FUNCTION_TRACER */
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