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[34.125.184.137]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b26eaf5cae2sm14584521a12.1.2025.05.24.10.41.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 24 May 2025 10:41:02 -0700 (PDT) Date: Sat, 24 May 2025 17:40:57 +0000 From: Carlos Llamas To: syzbot Cc: arve@android.com, brauner@kernel.org, gregkh@linuxfoundation.org, joelagnelf@nvidia.com, linux-kernel@vger.kernel.org, maco@android.com, surenb@google.com, syzkaller-bugs@googlegroups.com, tkjos@android.com Subject: Re: [syzbot] [kernel?] KASAN: slab-use-after-free Write in binder_remove_device Message-ID: References: <6831b67f.a70a0220.253bc2.006f.GAE@google.com> Precedence: bulk X-Mailing-List: linux-kernel@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: <6831b67f.a70a0220.253bc2.006f.GAE@google.com> On Sat, May 24, 2025 at 05:07:27AM -0700, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 176e917e010c Add linux-next specific files for 20250523 > git tree: linux-next > console+strace: https://syzkaller.appspot.com/x/log.txt?x=1399a170580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=e7902c752bef748 > dashboard link: https://syzkaller.appspot.com/bug?extid=4af454407ec393de51d6 > compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=108b55f4580000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1145e5f4580000 > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/5f7692c642fa/disk-176e917e.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/057a442d42d0/vmlinux-176e917e.xz > kernel image: https://storage.googleapis.com/syzbot-assets/8f8ebdb4dd96/bzImage-176e917e.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+4af454407ec393de51d6@syzkaller.appspotmail.com > Oh, I know what is happening here. I believe these would be the steps: 1. There are multiple devices in binder_devices. 2. 'binder_proc' of device X dies but its release is deferred. 3. binderfs is unmounted, decrements device X and waits. 4. 'binder_proc' is released, kfree's the device without removing it from the binder_devices list first. Leaves dangling pointers. 5. umount continues, releases next devices but list is corrupted. This should fix the problem... #syz test diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 8d9c5f436fca..6be0f7ac7213 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -5246,6 +5246,7 @@ static void binder_free_proc(struct binder_proc *proc) __func__, proc->outstanding_txns); device = container_of(proc->context, struct binder_device, context); if (refcount_dec_and_test(&device->ref)) { + binder_remove_device(device); kfree(proc->context->name); kfree(device); }