[PATCH] perf: fix use after free of perf_trace_buf

[Prateek Sood <prsood@codeaurora.org>]

SyS_perf_event_open()
  free_event()
    _free_event()
      tp_perf_event_destroy()
        perf_trace_destroy()
          perf_trace_event_unreg() //free perf_trace_buf

trace_cpu_frequency()
  perf_trace_cpu()
    perf_trace_buf_alloc() //access perf_trace_buf

	CPU0					CPU1
perf_trace_event_unreg()                perf_trace_cpu()
					head = (event_call->perf_events)

free_percpu(tp_event->perf_events)
tp_event->perf_events = NULL
--total_ref_count
free_percpu(perf_trace_buf[i])
perf_trace_buf[i] = NULL

					raw_data = perf_trace_buf[rctx]
					memset(raw_data)

A potential race exists between access of perf_trace_buf from
perf_trace_buf_alloc() and perf_trace_event_unreg(). This can
result in perf_trace_buf[rctx] being NULL during access from memset()
in perf_trace_buf_alloc().

Change-Id: I95ae774b9fcc653aa808f2d9f3e4359b3605e909
Signed-off-by: Prateek Sood <prsood@codeaurora.org>
---
 include/linux/trace_events.h    |  2 ++
 include/trace/perf.h            |  5 +++-
 kernel/trace/trace_event_perf.c | 63 ++++++++++++++++++++++++++++++++++-------
 kernel/trace/trace_kprobe.c     | 10 +++++--
 kernel/trace/trace_syscalls.c   | 14 ++++++---
 kernel/trace/trace_uprobe.c     |  2 ++
 6 files changed, 79 insertions(+), 17 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 8a62731..dbdad19 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -591,6 +591,8 @@ extern int  ftrace_profile_set_filter(struct perf_event *event, int event_id,
 extern void ftrace_profile_free_filter(struct perf_event *event);
 void perf_trace_buf_update(void *record, u16 type);
 void *perf_trace_buf_alloc(int size, struct pt_regs **regs, int *rctxp);
+void get_perf_trace_buf(void);
+void put_perf_trace_buf(void);
 
 void bpf_trace_run1(struct bpf_prog *prog, u64 arg1);
 void bpf_trace_run2(struct bpf_prog *prog, u64 arg1, u64 arg2);
diff --git a/include/trace/perf.h b/include/trace/perf.h
index dbc6c74..f808c33 100644
--- a/include/trace/perf.h
+++ b/include/trace/perf.h
@@ -55,9 +55,10 @@
 			     sizeof(u64));				\
 	__entry_size -= sizeof(u32);					\
 									\
+	get_perf_trace_buf();						\
 	entry = perf_trace_buf_alloc(__entry_size, &__regs, &rctx);	\
 	if (!entry)							\
-		return;							\
+		goto out;						\
 									\
 	perf_fetch_caller_regs(__regs);					\
 									\
@@ -68,6 +69,8 @@
 	perf_trace_run_bpf_submit(entry, __entry_size, rctx,		\
 				  event_call, __count, __regs,		\
 				  head, __task);			\
+out:									\
+	put_perf_trace_buf();						\
 }
 
 /*
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 4629a61..6caca88 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -21,7 +21,8 @@ typedef typeof(unsigned long [PERF_MAX_TRACE_SIZE / sizeof(unsigned long)])
 	perf_trace_t;
 
 /* Count the events in use (per event id, not per instance) */
-static int	total_ref_count;
+static int alloc_ref_count;
+static atomic_t access_ref_count[PERF_NR_CONTEXTS];
 
 static int perf_trace_event_perm(struct trace_event_call *tp_event,
 				 struct perf_event *p_event)
@@ -88,6 +89,34 @@ static int perf_trace_event_perm(struct trace_event_call *tp_event,
 	return 0;
 }
 
+void get_perf_trace_buf(void)
+{
+	int rctx;
+
+	rctx = perf_swevent_get_recursion_context();
+	if (rctx < 0)
+		return;
+
+	atomic_inc(&access_ref_count[rctx]);
+	perf_swevent_put_recursion_context(rctx);
+}
+EXPORT_SYMBOL_GPL(get_perf_trace_buf);
+NOKPROBE_SYMBOL(get_perf_trace_buf);
+
+void put_perf_trace_buf(void)
+{
+	int rctx;
+
+	rctx = perf_swevent_get_recursion_context();
+	if (rctx < 0)
+		return;
+
+	atomic_dec(&access_ref_count[rctx]);
+	perf_swevent_put_recursion_context(rctx);
+}
+EXPORT_SYMBOL_GPL(put_perf_trace_buf);
+NOKPROBE_SYMBOL(put_perf_trace_buf);
+
 static int perf_trace_event_reg(struct trace_event_call *tp_event,
 				struct perf_event *p_event)
 {
@@ -108,7 +137,7 @@ static int perf_trace_event_reg(struct trace_event_call *tp_event,
 
 	tp_event->perf_events = list;
 
-	if (!total_ref_count) {
+	if (!alloc_ref_count) {
 		char __percpu *buf;
 		int i;
 
@@ -125,11 +154,11 @@ static int perf_trace_event_reg(struct trace_event_call *tp_event,
 	if (ret)
 		goto fail;
 
-	total_ref_count++;
+	alloc_ref_count++;
 	return 0;
 
 fail:
-	if (!total_ref_count) {
+	if (!alloc_ref_count) {
 		int i;
 
 		for (i = 0; i < PERF_NR_CONTEXTS; i++) {
@@ -150,6 +179,7 @@ static void perf_trace_event_unreg(struct perf_event *p_event)
 {
 	struct trace_event_call *tp_event = p_event->tp_event;
 	int i;
+	bool retry;
 
 	if (--tp_event->perf_refcount > 0)
 		goto out;
@@ -165,10 +195,21 @@ static void perf_trace_event_unreg(struct perf_event *p_event)
 	free_percpu(tp_event->perf_events);
 	tp_event->perf_events = NULL;
 
-	if (!--total_ref_count) {
-		for (i = 0; i < PERF_NR_CONTEXTS; i++) {
-			free_percpu(perf_trace_buf[i]);
-			perf_trace_buf[i] = NULL;
+	if (!--alloc_ref_count) {
+again:
+		retry = false;
+		for (i = 0; (i < PERF_NR_CONTEXTS) && perf_trace_buf[i]; i++) {
+			if (!atomic_read(&access_ref_count[i])) {
+				free_percpu(perf_trace_buf[i]);
+				perf_trace_buf[i] = NULL;
+			} else
+				retry = true;
+		}
+
+		if (retry) {
+			set_current_state(TASK_INTERRUPTIBLE);
+			schedule_timeout(msecs_to_jiffies(1));
+			goto again;
 		}
 	}
 out:
@@ -453,15 +494,17 @@ void perf_trace_buf_update(void *record, u16 type)
 	memset(&regs, 0, sizeof(regs));
 	perf_fetch_caller_regs(&regs);
 
+	get_perf_trace_buf();
 	entry = perf_trace_buf_alloc(ENTRY_SIZE, NULL, &rctx);
 	if (!entry)
-		return;
+		goto out;
 
 	entry->ip = ip;
 	entry->parent_ip = parent_ip;
 	perf_trace_buf_submit(entry, ENTRY_SIZE, rctx, TRACE_FN,
 			      1, &regs, &head, NULL);
-
+out:
+	put_perf_trace_buf();
 #undef ENTRY_SIZE
 }
 
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 5d5129b..7830190 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1166,15 +1166,18 @@ static int kretprobe_event_define_fields(struct trace_event_call *event_call)
 	size = ALIGN(__size + sizeof(u32), sizeof(u64));
 	size -= sizeof(u32);
 
+	get_perf_trace_buf();
 	entry = perf_trace_buf_alloc(size, NULL, &rctx);
 	if (!entry)
-		return 0;
+		goto out;
 
 	entry->ip = (unsigned long)tk->rp.kp.addr;
 	memset(&entry[1], 0, dsize);
 	store_trace_args(&entry[1], &tk->tp, regs, sizeof(*entry), dsize);
 	perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
 			      head, NULL);
+out:
+	put_perf_trace_buf();
 	return 0;
 }
 NOKPROBE_SYMBOL(kprobe_perf_func);
@@ -1202,15 +1205,18 @@ static int kretprobe_event_define_fields(struct trace_event_call *event_call)
 	size = ALIGN(__size + sizeof(u32), sizeof(u64));
 	size -= sizeof(u32);
 
+	get_perf_trace_buf();
 	entry = perf_trace_buf_alloc(size, NULL, &rctx);
 	if (!entry)
-		return;
+		goto out;
 
 	entry->func = (unsigned long)tk->rp.kp.addr;
 	entry->ret_ip = (unsigned long)ri->ret_addr;
 	store_trace_args(&entry[1], &tk->tp, regs, sizeof(*entry), dsize);
 	perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
 			      head, NULL);
+out:
+	put_perf_trace_buf();
 }
 NOKPROBE_SYMBOL(kretprobe_perf_func);
 
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index f93a56d..a08110f 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -608,9 +608,10 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
 	size = ALIGN(size + sizeof(u32), sizeof(u64));
 	size -= sizeof(u32);
 
+	get_perf_trace_buf();
 	rec = perf_trace_buf_alloc(size, NULL, &rctx);
 	if (!rec)
-		return;
+		goto out;
 
 	rec->nr = syscall_nr;
 	syscall_get_arguments(current, regs, 0, sys_data->nb_args,
@@ -620,12 +621,14 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
 	     !perf_call_bpf_enter(sys_data->enter_event, regs, sys_data, rec)) ||
 	    hlist_empty(head)) {
 		perf_swevent_put_recursion_context(rctx);
-		return;
+		goto out;
 	}
 
 	perf_trace_buf_submit(rec, size, rctx,
 			      sys_data->enter_event->event.type, 1, regs,
 			      head, NULL);
+out:
+	put_perf_trace_buf();
 }
 
 static int perf_sysenter_enable(struct trace_event_call *call)
@@ -706,9 +709,10 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
 	size = ALIGN(sizeof(*rec) + sizeof(u32), sizeof(u64));
 	size -= sizeof(u32);
 
+	get_perf_trace_buf();
 	rec = perf_trace_buf_alloc(size, NULL, &rctx);
 	if (!rec)
-		return;
+		goto out;
 
 	rec->nr = syscall_nr;
 	rec->ret = syscall_get_return_value(current, regs);
@@ -717,11 +721,13 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
 	     !perf_call_bpf_exit(sys_data->exit_event, regs, rec)) ||
 	    hlist_empty(head)) {
 		perf_swevent_put_recursion_context(rctx);
-		return;
+		goto out;
 	}
 
 	perf_trace_buf_submit(rec, size, rctx, sys_data->exit_event->event.type,
 			      1, regs, head, NULL);
+out:
+	put_perf_trace_buf();
 }
 
 static int perf_sysexit_enable(struct trace_event_call *call)
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index be78d99..c931b22 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -1116,6 +1116,7 @@ static void __uprobe_perf_func(struct trace_uprobe *tu,
 	if (hlist_empty(head))
 		goto out;
 
+	get_perf_trace_buf();
 	entry = perf_trace_buf_alloc(size, NULL, &rctx);
 	if (!entry)
 		goto out;
@@ -1140,6 +1141,7 @@ static void __uprobe_perf_func(struct trace_uprobe *tu,
 	perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
 			      head, NULL);
  out:
+	put_perf_trace_buf();
 	preempt_enable();
 }
 
-- 
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