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From:   Mina Almasry <almasrymina@google.com>
Date:   Tue, 23 Apr 2019 14:31:26 -0700
Message-ID: <CAHS8izOeOe3wekn_TKFopNCVE1aq9J2-Vh17ivGr26AaKucsvQ@mail.gmail.com>
Subject: Re: [PATCH] fs: Fix ovl_i_mutex_dir_key/p->lock/cred cred_guard_mutex deadlock
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     overlayfs <linux-unionfs@vger.kernel.org>,
        Greg Thelen <gthelen@google.com>,
        Shakeel B <shakeelb@google.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        "open list:FILESYSTEMS (VFS and infrastructure)" 
        <linux-fsdevel@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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On Tue, Apr 23, 2019 at 7:28 AM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> 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
> >

Miklos, this patch is outdated, I've sent out v2 to the maintainer.
I'll forward that to linux-unionfs.