linux-kernel - [PATCH] kref: Avoid null pointer dereference after WARN

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Message-ID: <20170627035215.GA132342@beast>
Date:   Mon, 26 Jun 2017 20:52:15 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Daniel Micay <danielmicay@...il.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] kref: Avoid null pointer dereference after WARN

From: Daniel Micay <danielmicay@...il.com>

The WARN_ON() checking for a NULL release pointer should be a BUG()
since continuing with a NULL release pointer will lead to a NULL
pointer dereference anyway.

The kref_put() case is extracted from PaX, and Kees Cook noted it should
be extended to the other two cases.

Signed-off-by: Daniel Micay <danielmicay@...il.com>
[kees: clarify commit log]
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/kref.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/kref.h b/include/linux/kref.h
index f4156f88f557..82a2c225eae3 100644
--- a/include/linux/kref.h
+++ b/include/linux/kref.h
@@ -66,7 +66,7 @@ static inline void kref_get(struct kref *kref)
  */
 static inline int kref_put(struct kref *kref, void (*release)(struct kref *kref))
 {
-	WARN_ON(release == NULL);
+	BUG_ON(release == NULL);
 
 	if (refcount_dec_and_test(&kref->refcount)) {
 		release(kref);
@@ -79,7 +79,7 @@ static inline int kref_put_mutex(struct kref *kref,
 				 void (*release)(struct kref *kref),
 				 struct mutex *lock)
 {
-	WARN_ON(release == NULL);
+	BUG_ON(release == NULL);
 
 	if (refcount_dec_and_mutex_lock(&kref->refcount, lock)) {
 		release(kref);
@@ -92,7 +92,7 @@ static inline int kref_put_lock(struct kref *kref,
 				void (*release)(struct kref *kref),
 				spinlock_t *lock)
 {
-	WARN_ON(release == NULL);
+	BUG_ON(release == NULL);
 
 	if (refcount_dec_and_lock(&kref->refcount, lock)) {
 		release(kref);

-- 
Kees Cook
Pixel Security