Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933301AbeAAOrF (ORCPT + 1 other); Mon, 1 Jan 2018 09:47:05 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:46880 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933284AbeAAOrC (ORCPT ); Mon, 1 Jan 2018 09:47:02 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Todd Kjos Subject: [PATCH 4.14 134/146] binder: fix proc->files use-after-free Date: Mon, 1 Jan 2018 15:38:45 +0100 Message-Id: <20180101140143.141602864@linuxfoundation.org> X-Mailer: git-send-email 2.15.1 In-Reply-To: <20180101140123.743014891@linuxfoundation.org> References: <20180101140123.743014891@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Todd Kjos commit 7f3dc0088b98533f17128058fac73cd8b2752ef1 upstream. proc->files cleanup is initiated by binder_vma_close. Therefore a reference on the binder_proc is not enough to prevent the files_struct from being released while the binder_proc still has a reference. This can lead to an attempt to dereference the stale pointer obtained from proc->files prior to proc->files cleanup. This has been seen once in task_get_unused_fd_flags() when __alloc_fd() is called with a stale "files". The fix is to protect proc->files with a mutex to prevent cleanup while in use. Signed-off-by: Todd Kjos Signed-off-by: Greg Kroah-Hartman --- drivers/android/binder.c | 44 +++++++++++++++++++++++++++++++------------- 1 file changed, 31 insertions(+), 13 deletions(-) --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -482,7 +482,8 @@ enum binder_deferred_state { * @tsk task_struct for group_leader of process * (invariant after initialized) * @files files_struct for process - * (invariant after initialized) + * (protected by @files_lock) + * @files_lock mutex to protect @files * @deferred_work_node: element for binder_deferred_list * (protected by binder_deferred_lock) * @deferred_work: bitmap of deferred work to perform @@ -530,6 +531,7 @@ struct binder_proc { int pid; struct task_struct *tsk; struct files_struct *files; + struct mutex files_lock; struct hlist_node deferred_work_node; int deferred_work; bool is_dead; @@ -877,20 +879,26 @@ static void binder_inc_node_tmpref_ilock static int task_get_unused_fd_flags(struct binder_proc *proc, int flags) { - struct files_struct *files = proc->files; unsigned long rlim_cur; unsigned long irqs; + int ret; - if (files == NULL) - return -ESRCH; - - if (!lock_task_sighand(proc->tsk, &irqs)) - return -EMFILE; - + mutex_lock(&proc->files_lock); + if (proc->files == NULL) { + ret = -ESRCH; + goto err; + } + if (!lock_task_sighand(proc->tsk, &irqs)) { + ret = -EMFILE; + goto err; + } rlim_cur = task_rlimit(proc->tsk, RLIMIT_NOFILE); unlock_task_sighand(proc->tsk, &irqs); - return __alloc_fd(files, 0, rlim_cur, flags); + ret = __alloc_fd(proc->files, 0, rlim_cur, flags); +err: + mutex_unlock(&proc->files_lock); + return ret; } /* @@ -899,8 +907,10 @@ static int task_get_unused_fd_flags(stru static void task_fd_install( struct binder_proc *proc, unsigned int fd, struct file *file) { + mutex_lock(&proc->files_lock); if (proc->files) __fd_install(proc->files, fd, file); + mutex_unlock(&proc->files_lock); } /* @@ -910,9 +920,11 @@ static long task_close_fd(struct binder_ { int retval; - if (proc->files == NULL) - return -ESRCH; - + mutex_lock(&proc->files_lock); + if (proc->files == NULL) { + retval = -ESRCH; + goto err; + } retval = __close_fd(proc->files, fd); /* can't restart close syscall because file table entry was cleared */ if (unlikely(retval == -ERESTARTSYS || @@ -920,7 +932,8 @@ static long task_close_fd(struct binder_ retval == -ERESTARTNOHAND || retval == -ERESTART_RESTARTBLOCK)) retval = -EINTR; - +err: + mutex_unlock(&proc->files_lock); return retval; } @@ -4627,7 +4640,9 @@ static int binder_mmap(struct file *filp ret = binder_alloc_mmap_handler(&proc->alloc, vma); if (ret) return ret; + mutex_lock(&proc->files_lock); proc->files = get_files_struct(current); + mutex_unlock(&proc->files_lock); return 0; err_bad_arg: @@ -4651,6 +4666,7 @@ static int binder_open(struct inode *nod spin_lock_init(&proc->outer_lock); get_task_struct(current->group_leader); proc->tsk = current->group_leader; + mutex_init(&proc->files_lock); INIT_LIST_HEAD(&proc->todo); proc->default_priority = task_nice(current); binder_dev = container_of(filp->private_data, struct binder_device, @@ -4903,9 +4919,11 @@ static void binder_deferred_func(struct files = NULL; if (defer & BINDER_DEFERRED_PUT_FILES) { + mutex_lock(&proc->files_lock); files = proc->files; if (files) proc->files = NULL; + mutex_unlock(&proc->files_lock); } if (defer & BINDER_DEFERRED_FLUSH)