Cc: linux-unionfs On Thu, Apr 11, 2019 at 6:48 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> > --- > 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 >
