Re: [PATCH v2] fs: Fix ovl_i_mutex_dir_key/p->lock/cred cred_guard_mutex deadlock

From: Mina Almasry
Date: Fri May 10 2019 - 15:57:45 EST

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From: Mina Almasry <almasrymina@xxxxxxxxxx>
Date: Tue, Apr 23, 2019 at 2:32 PM
To: Mina Almasry, Greg Thelen, Shakeel B, overlayfs
Cc: Alexander Viro, open list:FILESYSTEMS (VFS and infrastructure), open list

> On Fri, Apr 12, 2019 at 4:11 PM Mina Almasry <almasrymina@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >
> > 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

Friendly ping on this review.

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