[PATCH v2] kasan: fix deadlock in start_report()

[Weizhao Ouyang]

From: Weizhao Ouyang <o451686892@xxxxxxxxx>

From: Shuai Yuan <yuanshuai@xxxxxxxx>

Calling start_report() again between start_report() and end_report()
will result in a race issue for the report_lock. In extreme cases this
problem arose in Kunit tests in the hardware tag-based Kasan mode.

For example, when an invalid memory release problem is found,
kasan_report_invalid_free() will print error log, but if an MTE exception
is raised during the output log, the kasan_report() is called, resulting
in a deadlock problem. The kasan_depth not protect it in hardware
tag-based Kasan mode.

Signed-off-by: Shuai Yuan <yuanshuai@xxxxxxxx>
Reviewed-by: Weizhao Ouyang <ouyangweizhao@xxxxxxxx>
Reviewed-by: Peng Ren <renlipeng@xxxxxxxx>
---
Changes in v2:
-- remove redundant log

 mm/kasan/report.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 22598b20c7b7..aa39aa8b1855 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -166,7 +166,7 @@ static inline void fail_non_kasan_kunit_test(void) { }
 
 static DEFINE_SPINLOCK(report_lock);
 
-static void start_report(unsigned long *flags, bool sync)
+static bool start_report(unsigned long *flags, bool sync)
 {
 	fail_non_kasan_kunit_test();
 	/* Respect the /proc/sys/kernel/traceoff_on_warning interface. */
@@ -175,8 +175,13 @@ static void start_report(unsigned long *flags, bool sync)
 	lockdep_off();
 	/* Make sure we don't end up in loop. */
 	kasan_disable_current();
-	spin_lock_irqsave(&report_lock, *flags);
+	if (!spin_trylock_irqsave(&report_lock, *flags)) {
+		lockdep_on();
+		kasan_enable_current();
+		return false;
+	}
 	pr_err("==================================================================\n");
+	return true;
 }
 
 static void end_report(unsigned long *flags, void *addr)
@@ -468,7 +473,10 @@ void kasan_report_invalid_free(void *ptr, unsigned long ip, enum kasan_report_ty
 	if (unlikely(!report_enabled()))
 		return;
 
-	start_report(&flags, true);
+	if (!start_report(&flags, true)) {
+		pr_err("%s: report ignore\n", __func__);
+		return;
+	}
 
 	memset(&info, 0, sizeof(info));
 	info.type = type;
@@ -503,7 +511,11 @@ bool kasan_report(unsigned long addr, size_t size, bool is_write,
 		goto out;
 	}
 
-	start_report(&irq_flags, true);
+	if (!start_report(&irq_flags, true)) {
+		ret = false;
+		pr_err("%s: report ignore\n", __func__);
+		goto out;
+	}
 
 	memset(&info, 0, sizeof(info));
 	info.type = KASAN_REPORT_ACCESS;
@@ -536,7 +548,10 @@ void kasan_report_async(void)
 	if (unlikely(!report_enabled()))
 		return;
 
-	start_report(&flags, false);
+	if (!start_report(&flags, false)) {
+		pr_err("%s: report ignore\n", __func__);
+		return;
+	}
 	pr_err("BUG: KASAN: invalid-access\n");
 	pr_err("Asynchronous fault: no details available\n");
 	pr_err("\n");
-- 
2.25.1