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Date: Tue, 23 Apr 2019 14:32:59 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Mina Almasry <almasrymina@...gle.com>,
Greg Thelen <gthelen@...gle.com>,
Shakeel B <shakeelb@...gle.com>,
overlayfs <linux-unionfs@...r.kernel.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
"open list:FILESYSTEMS (VFS and infrastructure)"
<linux-fsdevel@...r.kernel.org>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] fs: Fix ovl_i_mutex_dir_key/p->lock/cred
cred_guard_mutex deadlock
On Fri, Apr 12, 2019 at 4:11 PM Mina Almasry <almasrymina@...gle.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@...gle.com>
> ---
>
> v2: Fix wrong jump to wrong label on failure.
>
> fs/exec.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index 2e0033348d8e1..a23f2a7603eee 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_files;
> +
> 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;
> --
> 2.21.0.392.gf8f6787159e-goog
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