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 <almasrym...@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
