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Wed, 11 Jun 2025 12:15:09 -0700 (PDT) Received: from pc636 ([2001:9b1:d5a0:a500::800]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-55384f3deeesm1408927e87.62.2025.06.11.12.15.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Jun 2025 12:15:09 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 11 Jun 2025 21:15:07 +0200 To: syzbot Cc: akpm@linux-foundation.org, josh@joshtriplett.org, kent.overstreet@linux.dev, linux-bcachefs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, paulmck@kernel.org, rcu@vger.kernel.org, syzkaller-bugs@googlegroups.com, urezki@gmail.com Subject: Re: [syzbot] [bcachefs?] [rcu?] BUG: unable to handle kernel NULL pointer dereference in rcu_core (3) Message-ID: References: <6849c49b.a00a0220.1eb5f5.00f2.GAE@google.com> Precedence: bulk X-Mailing-List: linux-bcachefs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6849c49b.a00a0220.1eb5f5.00f2.GAE@google.com> On Wed, Jun 11, 2025 at 11:02:03AM -0700, syzbot wrote: > Hello, > > syzbot tried to test the proposed patch but the build/boot failed: > > failed to apply patch: > checking file kernel/rcu/tree.c > patch: **** unexpected end of file in patch > > > > Tested on: > > commit: aef17cb3 Revert "mm/damon/Kconfig: enable CONFIG_DAMON.. > git tree: upstream > kernel config: https://syzkaller.appspot.com/x/.config?x=523d3ff8e053340a > dashboard link: https://syzkaller.appspot.com/bug?extid=80e5d6f453f14a53383a > compiler: > patch: https://syzkaller.appspot.com/x/patch.diff?x=17de99d4580000 > #syz test diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e8a4b720d7d2..14d4499c6fc3 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3072,6 +3072,10 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in) /* Misaligned rcu_head! */ WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1)); + /* Avoid NULL dereference if callback is NULL. */ + if (WARN_ON_ONCE(!func)) + return; + if (debug_rcu_head_queue(head)) { /* * Probable double call_rcu(), so leak the callback.