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([2620:15c:2cd:203:5cdc:422c:7b28:ebb5]) by smtp.gmail.com with ESMTPSA id c81sm7331620pfb.107.2018.12.07.08.23.44 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 07 Dec 2018 08:23:45 -0800 (PST) Message-ID: <1544199824.185366.304.camel@acm.org> Subject: Re: [PATCH v3 16/24] locking/lockdep: Retain the class key and name while freeing a lock class From: Bart Van Assche To: Waiman Long , Peter Zijlstra Cc: mingo@redhat.com, tj@kernel.org, johannes.berg@intel.com, linux-kernel@vger.kernel.org, Johannes Berg Date: Fri, 07 Dec 2018 08:23:44 -0800 In-Reply-To: References: <20181207011148.251812-1-bvanassche@acm.org> <20181207011148.251812-17-bvanassche@acm.org> <20181207102143.GH2237@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-7" X-Mailer: Evolution 3.26.2-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2018-12-07 at 09:50 -0500, Waiman Long wrote: +AD4 On 12/07/2018 05:21 AM, Peter Zijlstra wrote: +AD4 +AD4 On Thu, Dec 06, 2018 at 05:11:40PM -0800, Bart Van Assche wrote: +AD4 +AD4 +AD4 The next patch in this series uses the class name in code that +AD4 +AD4 +AD4 detects calls to lock+AF8-acquire() while a class key is being freed. Hence +AD4 +AD4 +AD4 retain the class name for lock classes that are being freed. +AD4 +AD4 +AD4 +AD4 From readin the discussion with v2+ADs you meant to say: 'uses the class +AD4 +AD4 name pointer', right? You're not actually ever going to dereference it, +AD4 +AD4 since that would be a UaF. +AD4 +AD4 +AD4 +AD4 +AD4 Cc: Peter Zijlstra +ADw-peterz+AEA-infradead.org+AD4 +AD4 +AD4 +AD4 Cc: Waiman Long +ADw-longman+AEA-redhat.com+AD4 +AD4 +AD4 +AD4 Cc: Johannes Berg +ADw-johannes+AEA-sipsolutions.net+AD4 +AD4 +AD4 +AD4 Signed-off-by: Bart Van Assche +ADw-bvanassche+AEA-acm.org+AD4 +AD4 +AD4 +AD4 --- +AD4 +AD4 +AD4 kernel/locking/lockdep.c +AHw 4 +---- +AD4 +AD4 +AD4 1 file changed, 1 insertion(+-), 3 deletions(-) +AD4 +AD4 +AD4 +AD4 +AD4 +AD4 diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c +AD4 +AD4 +AD4 index ecd92969674c..92bdb187987f 100644 +AD4 +AD4 +AD4 --- a/kernel/locking/lockdep.c +AD4 +AD4 +AD4 +-+-+- b/kernel/locking/lockdep.c +AD4 +AD4 +AD4 +AEAAQA -4147,10 +-4147,8 +AEAAQA static void zap+AF8-class(struct lock+AF8-class +ACo-class) +AD4 +AD4 +AD4 +ACo Unhash the class and remove it from the all+AF8-lock+AF8-classes list: +AD4 +AD4 +AD4 +ACo-/ +AD4 +AD4 +AD4 hlist+AF8-del+AF8-rcu(+ACY-class-+AD4-hash+AF8-entry)+ADs +AD4 +AD4 +AD4 +- class-+AD4-hash+AF8-entry.pprev +AD0 NULL+ADs +AD4 +AD4 +AD4 list+AF8-del(+ACY-class-+AD4-lock+AF8-entry)+ADs +AD4 +AD4 +AD4 - +AD4 +AD4 +AD4 - RCU+AF8-INIT+AF8-POINTER(class-+AD4-key, NULL)+ADs +AD4 +AD4 +AD4 - RCU+AF8-INIT+AF8-POINTER(class-+AD4-name, NULL)+ADs +AD4 +AD4 +AD4 +AH0 +AD4 +AD4 +AD4 +AD4 +AD4 +AD4 static inline int within(const void +ACo-addr, void +ACo-start, unsigned long size) +AD4 +AD4 +AD4 -- +AD4 +AD4 +AD4 2.20.0.rc2.403.gdbc3b29805-goog +AD4 +AD4 +AD4 +AD4 +AD4 I still prefer keeping the clearing statements. Leaving key behind +AD4 should be OK as it is just a long value to be compared against. The +AD4 variable name is a different story as it is a pointer that will +AD4 reference bytes that it points to unless you save the name in a safe +AD4 storage area and change the pointer to point there. I will drop this patch and update later patches accordingly. Bart.