From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 31758C4361A for ; Thu, 3 Dec 2020 20:13:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B9386207B8 for ; Thu, 3 Dec 2020 20:13:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726667AbgLCUNQ (ORCPT ); Thu, 3 Dec 2020 15:13:16 -0500 Received: from out02.mta.xmission.com ([166.70.13.232]:55970 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726681AbgLCUNQ (ORCPT ); Thu, 3 Dec 2020 15:13:16 -0500 Received: from in02.mta.xmission.com ([166.70.13.52]) by out02.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1kkuxu-007jhv-Um; Thu, 03 Dec 2020 13:12:35 -0700 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1kkuxs-00B3Q7-T7; Thu, 03 Dec 2020 13:12:34 -0700 From: ebiederm@xmission.com (Eric W. Biederman) To: Cc: Linus Torvalds , Peter Zijlstra , Ingo Molnar , Will Deacon , Jann Horn , Vasiliy Kulikov , Al Viro , Bernd Edlinger , Oleg Nesterov , Christopher Yeoh , Cyrill Gorcunov , Sargun Dhillon , Christian Brauner , Arnd Bergmann , Arnaldo Carvalho de Melo References: <87tut2bqik.fsf@x220.int.ebiederm.org> Date: Thu, 03 Dec 2020 14:12:00 -0600 In-Reply-To: <87tut2bqik.fsf@x220.int.ebiederm.org> (Eric W. Biederman's message of "Thu, 03 Dec 2020 14:09:39 -0600") Message-ID: <87ft4mbqen.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1kkuxs-00B3Q7-T7;;;mid=<87ft4mbqen.fsf@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1/rN3wMRrWj4Xqx12BfsMhjpGPyiX/i1Dg= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: [PATCH 3/3] exec: Transform exec_update_mutex into a rw_semaphore X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Recently syzbot reported[0] that there is a deadlock amongst the users of exec_update_mutex. The problematic lock ordering found by lockdep was: perf_event_open (exec_update_mutex -> ovl_i_mutex) chown (ovl_i_mutex -> sb_writes) sendfile (sb_writes -> p->lock) by reading from a proc file and writing to overlayfs proc_pid_syscall (p->lock -> exec_update_mutex) While looking at possible solutions it occured to me that all of the users and possible users involved only wanted to state of the given process to remain the same. They are all readers. The only writer is exec. There is no reason for readers to block on each other. So fix this deadlock by transforming exec_update_mutex into a rw_semaphore named exec_update_lock that only exec takes for writing. Cc: Jann Horn Cc: Vasiliy Kulikov Cc: Al Viro Cc: Bernd Edlinger Cc: Oleg Nesterov Cc: Christopher Yeoh Cc: Cyrill Gorcunov Cc: Sargun Dhillon Cc: Christian Brauner Cc: Arnd Bergmann Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Arnaldo Carvalho de Melo Fixes: eea9673250db ("exec: Add exec_update_mutex to replace cred_guard_mutex") [0] https://lkml.kernel.org/r/00000000000063640c05ade8e3de@google.com Reported-by: syzbot+db9cdf3dd1f64252c6ef@syzkaller.appspotmail.com Signed-off-by: Eric W. Biederman --- fs/exec.c | 12 ++++++------ fs/proc/base.c | 10 +++++----- include/linux/sched/signal.h | 11 ++++++----- init/init_task.c | 2 +- kernel/events/core.c | 12 ++++++------ kernel/fork.c | 6 +++--- kernel/kcmp.c | 30 +++++++++++++++--------------- kernel/pid.c | 4 ++-- 8 files changed, 44 insertions(+), 43 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 9e9368603168..b822aa0d682e 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -965,8 +965,8 @@ EXPORT_SYMBOL(read_code); /* * Maps the mm_struct mm into the current task struct. - * On success, this function returns with the mutex - * exec_update_mutex locked. + * On success, this function returns with exec_update_lock + * held for writing. */ static int exec_mmap(struct mm_struct *mm) { @@ -981,7 +981,7 @@ static int exec_mmap(struct mm_struct *mm) if (old_mm) sync_mm_rss(old_mm); - ret = mutex_lock_killable(&tsk->signal->exec_update_mutex); + ret = down_write_killable(&tsk->signal->exec_update_lock); if (ret) return ret; @@ -995,7 +995,7 @@ static int exec_mmap(struct mm_struct *mm) mmap_read_lock(old_mm); if (unlikely(old_mm->core_state)) { mmap_read_unlock(old_mm); - mutex_unlock(&tsk->signal->exec_update_mutex); + up_write(&tsk->signal->exec_update_lock); return -EINTR; } } @@ -1392,7 +1392,7 @@ int begin_new_exec(struct linux_binprm * bprm) return 0; out_unlock: - mutex_unlock(&me->signal->exec_update_mutex); + up_write(&me->signal->exec_update_lock); out: return retval; } @@ -1433,7 +1433,7 @@ void setup_new_exec(struct linux_binprm * bprm) * some architectures like powerpc */ me->mm->task_size = TASK_SIZE; - mutex_unlock(&me->signal->exec_update_mutex); + up_write(&me->signal->exec_update_lock); mutex_unlock(&me->signal->cred_guard_mutex); } EXPORT_SYMBOL(setup_new_exec); diff --git a/fs/proc/base.c b/fs/proc/base.c index 0f707003dda5..dd1f4f6f22bc 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -405,11 +405,11 @@ static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns, static int lock_trace(struct task_struct *task) { - int err = mutex_lock_killable(&task->signal->exec_update_mutex); + int err = down_read_killable(&task->signal->exec_update_lock); if (err) return err; if (!ptrace_may_access(task, PTRACE_MODE_ATTACH_FSCREDS)) { - mutex_unlock(&task->signal->exec_update_mutex); + up_read(&task->signal->exec_update_lock); return -EPERM; } return 0; @@ -417,7 +417,7 @@ static int lock_trace(struct task_struct *task) static void unlock_trace(struct task_struct *task) { - mutex_unlock(&task->signal->exec_update_mutex); + up_read(&task->signal->exec_update_lock); } #ifdef CONFIG_STACKTRACE @@ -2928,7 +2928,7 @@ static int do_io_accounting(struct task_struct *task, struct seq_file *m, int wh unsigned long flags; int result; - result = mutex_lock_killable(&task->signal->exec_update_mutex); + result = down_read_killable(&task->signal->exec_update_lock); if (result) return result; @@ -2964,7 +2964,7 @@ static int do_io_accounting(struct task_struct *task, struct seq_file *m, int wh result = 0; out_unlock: - mutex_unlock(&task->signal->exec_update_mutex); + up_read(&task->signal->exec_update_lock); return result; } diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index 1bad18a1d8ba..4b6a8234d7fc 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -228,12 +228,13 @@ struct signal_struct { * credential calculations * (notably. ptrace) * Deprecated do not use in new code. - * Use exec_update_mutex instead. - */ - struct mutex exec_update_mutex; /* Held while task_struct is being - * updated during exec, and may have - * inconsistent permissions. + * Use exec_update_lock instead. */ + struct rw_semaphore exec_update_lock; /* Held while task_struct is + * being updated during exec, + * and may have inconsistent + * permissions. + */ } __randomize_layout; /* diff --git a/init/init_task.c b/init/init_task.c index a56f0abb63e9..15f6eb93a04f 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -26,7 +26,7 @@ static struct signal_struct init_signals = { .multiprocess = HLIST_HEAD_INIT, .rlim = INIT_RLIMITS, .cred_guard_mutex = __MUTEX_INITIALIZER(init_signals.cred_guard_mutex), - .exec_update_mutex = __MUTEX_INITIALIZER(init_signals.exec_update_mutex), + .exec_update_lock = __RWSEM_INITIALIZER(init_signals.exec_update_lock), #ifdef CONFIG_POSIX_TIMERS .posix_timers = LIST_HEAD_INIT(init_signals.posix_timers), .cputimer = { diff --git a/kernel/events/core.c b/kernel/events/core.c index da467e1dd49a..3189f690236e 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1325,7 +1325,7 @@ static void put_ctx(struct perf_event_context *ctx) * function. * * Lock order: - * exec_update_mutex + * exec_update_lock * task_struct::perf_event_mutex * perf_event_context::mutex * perf_event::child_mutex; @@ -11730,14 +11730,14 @@ SYSCALL_DEFINE5(perf_event_open, } if (task) { - err = mutex_lock_interruptible(&task->signal->exec_update_mutex); + err = down_read_interruptible(&task->signal->exec_update_lock); if (err) goto err_task; /* * Preserve ptrace permission check for backwards compatibility. * - * We must hold exec_update_mutex across this and any potential + * We must hold exec_update_lock across this and any potential * perf_install_in_context() call for this new event to * serialize against exec() altering our credentials (and the * perf_event_exit_task() that could imply). @@ -12026,7 +12026,7 @@ SYSCALL_DEFINE5(perf_event_open, mutex_unlock(&ctx->mutex); if (task) { - mutex_unlock(&task->signal->exec_update_mutex); + up_read(&task->signal->exec_update_lock); put_task_struct(task); } @@ -12062,7 +12062,7 @@ SYSCALL_DEFINE5(perf_event_open, free_event(event); err_cred: if (task) - mutex_unlock(&task->signal->exec_update_mutex); + up_read(&task->signal->exec_update_lock); err_task: if (task) put_task_struct(task); @@ -12367,7 +12367,7 @@ static void perf_event_exit_task_context(struct task_struct *child, int ctxn) /* * When a child task exits, feed back event values to parent events. * - * Can be called with exec_update_mutex held when called from + * Can be called with exec_update_lock held when called from * setup_new_exec(). */ void perf_event_exit_task(struct task_struct *child) diff --git a/kernel/fork.c b/kernel/fork.c index 837b546528c8..4d0ae6f827df 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1221,7 +1221,7 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode) struct mm_struct *mm; int err; - err = mutex_lock_killable(&task->signal->exec_update_mutex); + err = down_read_killable(&task->signal->exec_update_lock); if (err) return ERR_PTR(err); @@ -1231,7 +1231,7 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode) mmput(mm); mm = ERR_PTR(-EACCES); } - mutex_unlock(&task->signal->exec_update_mutex); + up_read(&task->signal->exec_update_lock); return mm; } @@ -1591,7 +1591,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk) sig->oom_score_adj_min = current->signal->oom_score_adj_min; mutex_init(&sig->cred_guard_mutex); - mutex_init(&sig->exec_update_mutex); + init_rwsem(&sig->exec_update_lock); return 0; } diff --git a/kernel/kcmp.c b/kernel/kcmp.c index 36e58eb5a11d..5353edfad8e1 100644 --- a/kernel/kcmp.c +++ b/kernel/kcmp.c @@ -70,25 +70,25 @@ get_file_raw_ptr(struct task_struct *task, unsigned int idx) return file; } -static void kcmp_unlock(struct mutex *m1, struct mutex *m2) +static void kcmp_unlock(struct rw_semaphore *l1, struct rw_semaphore *l2) { - if (likely(m2 != m1)) - mutex_unlock(m2); - mutex_unlock(m1); + if (likely(l2 != l1)) + up_read(l2); + up_read(l1); } -static int kcmp_lock(struct mutex *m1, struct mutex *m2) +static int kcmp_lock(struct rw_semaphore *l1, struct rw_semaphore *l2) { int err; - if (m2 > m1) - swap(m1, m2); + if (l2 > l1) + swap(l1, l2); - err = mutex_lock_killable(m1); - if (!err && likely(m1 != m2)) { - err = mutex_lock_killable_nested(m2, SINGLE_DEPTH_NESTING); + err = down_read_killable(l1); + if (!err && likely(l1 != l2)) { + err = down_read_killable_nested(l2, SINGLE_DEPTH_NESTING); if (err) - mutex_unlock(m1); + up_read(l1); } return err; @@ -156,8 +156,8 @@ SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type, /* * One should have enough rights to inspect task details. */ - ret = kcmp_lock(&task1->signal->exec_update_mutex, - &task2->signal->exec_update_mutex); + ret = kcmp_lock(&task1->signal->exec_update_lock, + &task2->signal->exec_update_lock); if (ret) goto err; if (!ptrace_may_access(task1, PTRACE_MODE_READ_REALCREDS) || @@ -212,8 +212,8 @@ SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type, } err_unlock: - kcmp_unlock(&task1->signal->exec_update_mutex, - &task2->signal->exec_update_mutex); + kcmp_unlock(&task1->signal->exec_update_lock, + &task2->signal->exec_update_lock); err: put_task_struct(task1); put_task_struct(task2); diff --git a/kernel/pid.c b/kernel/pid.c index a96bc4bf4f86..4856818c9de1 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -628,7 +628,7 @@ static struct file *__pidfd_fget(struct task_struct *task, int fd) struct file *file; int ret; - ret = mutex_lock_killable(&task->signal->exec_update_mutex); + ret = down_read_killable(&task->signal->exec_update_lock); if (ret) return ERR_PTR(ret); @@ -637,7 +637,7 @@ static struct file *__pidfd_fget(struct task_struct *task, int fd) else file = ERR_PTR(-EPERM); - mutex_unlock(&task->signal->exec_update_mutex); + up_read(&task->signal->exec_update_lock); return file ?: ERR_PTR(-EBADF); } -- 2.25.0