syzbot

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)

======================================================
WARNING: possible circular locking dependency detected
4.17.0-rc2+ #22 Not tainted
------------------------------------------------------
syz-executor762/4537 is trying to acquire lock:
        (ptrval) (&mm->mmap_sem){++++}, at: __might_fault+0xfb/0x1e0 mm/memory.c:4554

but task is already holding lock:
        (ptrval) (sk_lock-AF_INET6){+.+.}, at: lock_sock include/net/sock.h:1469 [inline]
        (ptrval) (sk_lock-AF_INET6){+.+.}, at: do_ipv6_setsockopt.isra.9+0x576/0x4680 net/ipv6/ipv6_sockglue.c:167

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (sk_lock-AF_INET6){+.+.}:
       lock_sock_nested+0xd0/0x120 net/core/sock.c:2844
       lock_sock include/net/sock.h:1469 [inline]
       tcp_mmap+0x1c7/0x14f0 net/ipv4/tcp.c:1759
       sock_mmap+0x8e/0xc0 net/socket.c:1144
       call_mmap include/linux/fs.h:1789 [inline]
       mmap_region+0xd13/0x1820 mm/mmap.c:1723
       do_mmap+0xc79/0x11d0 mm/mmap.c:1494
       do_mmap_pgoff include/linux/mm.h:2237 [inline]
       vm_mmap_pgoff+0x1fb/0x2a0 mm/util.c:357
       ksys_mmap_pgoff+0x4c9/0x640 mm/mmap.c:1544
       __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
       __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
       __x64_sys_mmap+0xe9/0x1b0 arch/x86/kernel/sys_x86_64.c:91
       do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&mm->mmap_sem){++++}:
       lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
       __might_fault+0x155/0x1e0 mm/memory.c:4555
       _copy_from_user+0x30/0x150 lib/usercopy.c:10
       copy_from_user include/linux/uaccess.h:147 [inline]
       do_ipv6_setsockopt.isra.9+0x29ab/0x4680 net/ipv6/ipv6_sockglue.c:677
       ipv6_setsockopt+0xbd/0x170 net/ipv6/ipv6_sockglue.c:922
       tcp_setsockopt+0x93/0xe0 net/ipv4/tcp.c:3029
       sock_common_setsockopt+0x9a/0xe0 net/core/sock.c:3042
       __sys_setsockopt+0x1bd/0x390 net/socket.c:1903
       __do_sys_setsockopt net/socket.c:1914 [inline]
       __se_sys_setsockopt net/socket.c:1911 [inline]
       __x64_sys_setsockopt+0xbe/0x150 net/socket.c:1911
       do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(sk_lock-AF_INET6);
                               lock(&mm->mmap_sem);
                               lock(sk_lock-AF_INET6);
  lock(&mm->mmap_sem);

 *** DEADLOCK ***

2 locks held by syz-executor762/4537:
 #0:         (ptrval) (rtnl_mutex){+.+.}, at: rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
 #1:         (ptrval) (sk_lock-AF_INET6){+.+.}, at: lock_sock include/net/sock.h:1469 [inline]
 #1:         (ptrval) (sk_lock-AF_INET6){+.+.}, at: do_ipv6_setsockopt.isra.9+0x576/0x4680 net/ipv6/ipv6_sockglue.c:167

stack backtrace:
CPU: 1 PID: 4537 Comm: syz-executor762 Not tainted 4.17.0-rc2+ #22
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1b9/0x294 lib/dump_stack.c:113
 print_circular_bug.isra.36.cold.54+0x1bd/0x27d kernel/locking/lockdep.c:1223
 check_prev_add kernel/locking/lockdep.c:1863 [inline]
 check_prevs_add kernel/locking/lockdep.c:1976 [inline]
 validate_chain kernel/locking/lockdep.c:2417 [inline]
 __lock_acquire+0x343e/0x5140 kernel/locking/lockdep.c:3431
 lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
 __might_fault+0x155/0x1e0 mm/memory.c:4555
 _copy_from_user+0x30/0x150 lib/usercopy.c:10
 copy_from_user include/linux/uaccess.h:147 [inline]
 do_ipv6_setsockopt.isra.9+0x29ab/0x4680 net/ipv6/ipv6_sockglue.c:677
 ipv6_setsockopt+0xbd/0x170 net/ipv6/ipv6_sockglue.c:922
 tcp_setsockopt+0x93/0xe0 net/ipv4/tcp.c:3029
 sock_common_setsockopt+0x9a/0xe0 net/core/sock.c:3042
 __sys_setsockopt+0x1bd/0x390 net/socket.c:1903
 __do_sys_setsockopt net/socket.c:1914 [inline]
 __se_sys_setsockopt net/socket.c:1911 [inline]
 __x64_sys_setsockopt+0xbe/0x150 net/socket.c:1911
 do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x43fdc9
RSP: 002b:00007ffdde7387f8 EFLAGS: 00000217 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RB