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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Tue, 23 Apr 2019 16:28:31 +0200
Message-ID: <CAJfpegsE+NOuR-mM752cBoBwbQF8X5jAkwTKZbn_Xg-mHskA6A@mail.gmail.com>
Subject: Re: [PATCH] fs: Fix ovl_i_mutex_dir_key/p->lock/cred cred_guard_mutex deadlock
To:     overlayfs <linux-unionfs@vger.kernel.org>
Cc:     Greg Thelen <gthelen@google.com>, Shakeel B <shakeelb@google.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Mina Almasry <almasrymina@google.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Cc: linux-unionfs

On Thu, Apr 11, 2019 at 6:48 PM Mina Almasry <almasrymina@google.com> wrote:
>
> These 3 locks are acquired simultaneously in different order causing
> deadlock:
>
> https://syzkaller.appspot.com/bug?id=00f119b8bb35a3acbcfafb9d36a2752b364e8d66
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.19.0-rc5+ #253 Not tainted
> ------------------------------------------------------
> syz-executor1/545 is trying to acquire lock:
> 00000000b04209e4 (&ovl_i_mutex_dir_key[depth]){++++}, at: inode_lock_shared include/linux/fs.h:748 [inline]
> 00000000b04209e4 (&ovl_i_mutex_dir_key[depth]){++++}, at: do_last fs/namei.c:3323 [inline]
> 00000000b04209e4 (&ovl_i_mutex_dir_key[depth]){++++}, at: path_openat+0x250d/0x5160 fs/namei.c:3534
>
> but task is already holding lock:
> 0000000044500cca (&sig->cred_guard_mutex){+.+.}, at: prepare_bprm_creds+0x53/0x120 fs/exec.c:1404
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #3 (&sig->cred_guard_mutex){+.+.}:
>        __mutex_lock_common kernel/locking/mutex.c:925 [inline]
>        __mutex_lock+0x166/0x1700 kernel/locking/mutex.c:1072
>        mutex_lock_killable_nested+0x16/0x20 kernel/locking/mutex.c:1102
>        lock_trace+0x4c/0xe0 fs/proc/base.c:384
>        proc_pid_stack+0x196/0x3b0 fs/proc/base.c:420
>        proc_single_show+0x101/0x190 fs/proc/base.c:723
>        seq_read+0x4af/0x1150 fs/seq_file.c:229
>        do_loop_readv_writev fs/read_write.c:700 [inline]
>        do_iter_read+0x4a3/0x650 fs/read_write.c:924
>        vfs_readv+0x175/0x1c0 fs/read_write.c:986
>        do_preadv+0x1cc/0x280 fs/read_write.c:1070
>        __do_sys_preadv fs/read_write.c:1120 [inline]
>        __se_sys_preadv fs/read_write.c:1115 [inline]
>        __x64_sys_preadv+0x9a/0xf0 fs/read_write.c:1115
>        do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>        entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> -> #2 (&p->lock){+.+.}:
>        __mutex_lock_common kernel/locking/mutex.c:925 [inline]
>        __mutex_lock+0x166/0x1700 kernel/locking/mutex.c:1072
>        mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
>        seq_read+0x71/0x1150 fs/seq_file.c:161
>        do_loop_readv_writev fs/read_write.c:700 [inline]
>        do_iter_read+0x4a3/0x650 fs/read_write.c:924
>        vfs_readv+0x175/0x1c0 fs/read_write.c:986
>        kernel_readv fs/splice.c:362 [inline]
>        default_file_splice_read+0x53c/0xb20 fs/splice.c:417
>        do_splice_to+0x12e/0x190 fs/splice.c:881
>        splice_direct_to_actor+0x270/0x8f0 fs/splice.c:953
>        do_splice_direct+0x2d4/0x420 fs/splice.c:1062
>        do_sendfile+0x62a/0xe20 fs/read_write.c:1440
>        __do_sys_sendfile64 fs/read_write.c:1495 [inline]
>        __se_sys_sendfile64 fs/read_write.c:1487 [inline]
>        __x64_sys_sendfile64+0x15d/0x250 fs/read_write.c:1487
>        do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>        entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> -> #1 (sb_writers#5){.+.+}:
>        percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36 [inline]
>        percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
>        __sb_start_write+0x214/0x370 fs/super.c:1387
>        sb_start_write include/linux/fs.h:1566 [inline]
>        mnt_want_write+0x3f/0xc0 fs/namespace.c:360
>        ovl_want_write+0x76/0xa0 fs/overlayfs/util.c:24
>        ovl_create_object+0x142/0x3a0 fs/overlayfs/dir.c:596
>        ovl_create+0x2b/0x30 fs/overlayfs/dir.c:627
>        lookup_open+0x1319/0x1b90 fs/namei.c:3234
>        do_last fs/namei.c:3324 [inline]
>        path_openat+0x15e7/0x5160 fs/namei.c:3534
>        do_filp_open+0x255/0x380 fs/namei.c:3564
>        do_sys_open+0x568/0x700 fs/open.c:1063
>        ksys_open include/linux/syscalls.h:1276 [inline]
>        __do_sys_creat fs/open.c:1121 [inline]
>        __se_sys_creat fs/open.c:1119 [inline]
>        __x64_sys_creat+0x61/0x80 fs/open.c:1119
>        do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>        entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> -> #0 (&ovl_i_mutex_dir_key[depth]){++++}:
>        lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3900
>        down_read+0xb0/0x1d0 kernel/locking/rwsem.c:24
>        inode_lock_shared include/linux/fs.h:748 [inline]
>        do_last fs/namei.c:3323 [inline]
>        path_openat+0x250d/0x5160 fs/namei.c:3534
>        do_filp_open+0x255/0x380 fs/namei.c:3564
>        do_open_execat+0x221/0x8e0 fs/exec.c:853
>        __do_execve_file.isra.33+0x173f/0x2540 fs/exec.c:1755
>        do_execveat_common fs/exec.c:1866 [inline]
>        do_execve fs/exec.c:1883 [inline]
>        __do_sys_execve fs/exec.c:1964 [inline]
>        __se_sys_execve fs/exec.c:1959 [inline]
>        __x64_sys_execve+0x8f/0xc0 fs/exec.c:1959
>        do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>        entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> other info that might help us debug this:
>
> Chain exists of:
>   &ovl_i_mutex_dir_key[depth] --> &p->lock --> &sig->cred_guard_mutex
>
>  Possible unsafe locking scenario:
>
>        CPU0                    CPU1
>        ----                    ----
>   lock(&sig->cred_guard_mutex);
>                                lock(&p->lock);
>                                lock(&sig->cred_guard_mutex);
>   lock(&ovl_i_mutex_dir_key[depth]);
>
>  *** DEADLOCK ***
>
> Solution: I establish this locking order for these locks:
>
> 1. ovl_i_mutex_dir_key
> 2. p->lock
> 3. sig->cred_guard_mutex
>
> In this change i fix the locking order of exec.c, which is the only
> instance that voilates this order.
>
> Signed-off-by: Mina Almasry <almasrymina@google.com>
> ---
>  fs/exec.c | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index 2e0033348d8e..423d90bc75cc 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1742,6 +1742,12 @@ static int __do_execve_file(int fd, struct filename *filename,
>         if (retval)
>                 goto out_ret;
>
> +       if (!file)
> +               file = do_open_execat(fd, filename, flags);
> +       retval = PTR_ERR(file);
> +       if (IS_ERR(file))
> +               goto out_free;
> +
>         retval = -ENOMEM;
>         bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
>         if (!bprm)
> @@ -1754,12 +1760,6 @@ static int __do_execve_file(int fd, struct filename *filename,
>         check_unsafe_exec(bprm);
>         current->in_execve = 1;
>
> -       if (!file)
> -               file = do_open_execat(fd, filename, flags);
> -       retval = PTR_ERR(file);
> -       if (IS_ERR(file))
> -               goto out_unmark;
> -
>         sched_exec();
>
>         bprm->file = file;
> @@ -1775,7 +1775,7 @@ static int __do_execve_file(int fd, struct filename *filename,
>                                             fd, filename->name);
>                 if (!pathbuf) {
>                         retval = -ENOMEM;
> -                       goto out_unmark;
> +                       goto out_free;
>                 }
>                 /*
>                  * Record that a name derived from an O_CLOEXEC fd will be
> @@ -1790,7 +1790,7 @@ static int __do_execve_file(int fd, struct filename *filename,
>
>         retval = bprm_mm_init(bprm);
>         if (retval)
> -               goto out_unmark;
> +               goto out_free;
>
>         retval = prepare_arg_pages(bprm, argv, envp);
>         if (retval < 0)
> @@ -1840,10 +1840,6 @@ static int __do_execve_file(int fd, struct filename *filename,
>                 mmput(bprm->mm);
>         }
>
> -out_unmark:
> -       current->fs->in_exec = 0;
> -       current->in_execve = 0;
> -
>  out_free:
>         free_bprm(bprm);
>         kfree(pathbuf);
> --
> 2.21.0.392.gf8f6787159e-goog
>