linux-kernel - [PATCH 4/4] kasan: Prevent deadlock in kasan reporting

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Message-Id: <1441266863-5435-4-git-send-email-aneesh.kumar@linux.vnet.ibm.com>
Date:	Thu,  3 Sep 2015 13:24:23 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	akpm@...ux-foundation.org, Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: [PATCH 4/4] kasan: Prevent deadlock in kasan reporting

We we end up calling kasan_report in real mode, our shadow mapping
for even spinlock variable will show poisoned. This will result
in us calling kasan_report_error with lock_report spin lock held.
To prevent this disable kasan reporting when we are priting
error w.r.t kasan.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
---
 mm/kasan/report.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 440bda3a3ecd..8c409b1664c8 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -173,12 +173,10 @@ static void print_shadow_for_address(const void *addr)
 		 * function, because generic functions may try to
 		 * access kasan mapping for the passed address.
 		 */
-		kasan_disable_current();
 		memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
 		print_hex_dump(KERN_ERR, buffer,
 			DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
 			shadow_buf, SHADOW_BYTES_PER_ROW, 0);
-		kasan_enable_current();
 
 		if (row_is_guilty(shadow_row, shadow))
 			pr_err("%*c\n",
@@ -195,6 +193,10 @@ void kasan_report_error(struct kasan_access_info *info)
 {
 	unsigned long flags;
 
+	/*
+	 * Make sure we don't end up in loop.
+	 */
+	kasan_disable_current();
 	spin_lock_irqsave(&report_lock, flags);
 	pr_err("================================="
 		"=================================\n");
@@ -204,12 +206,17 @@ void kasan_report_error(struct kasan_access_info *info)
 	pr_err("================================="
 		"=================================\n");
 	spin_unlock_irqrestore(&report_lock, flags);
+	kasan_enable_current();
 }
 
 void kasan_report_user_access(struct kasan_access_info *info)
 {
 	unsigned long flags;
 
+	/*
+	 * Make sure we don't end up in loop.
+	 */
+	kasan_disable_current();
 	spin_lock_irqsave(&report_lock, flags);
 	pr_err("================================="
 		"=================================\n");
@@ -222,6 +229,7 @@ void kasan_report_user_access(struct kasan_access_info *info)
 	pr_err("================================="
 		"=================================\n");
 	spin_unlock_irqrestore(&report_lock, flags);
+	kasan_enable_current();
 }
 
 void kasan_report(unsigned long addr, size_t size,
-- 
2.5.0

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