[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 14.973501] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 19.173088] random: sshd: uninitialized urandom read (32 bytes read) [ 19.540297] random: sshd: uninitialized urandom read (32 bytes read) [ 20.570264] random: sshd: uninitialized urandom read (32 bytes read) [ 25.604611] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.0.49' (ECDSA) to the list of known hosts. [ 31.165722] random: sshd: uninitialized urandom read (32 bytes read) executing program [ 31.296135] ================================================================== [ 31.303515] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 31.310759] Read of size 4 at addr ffff8801c7e4e500 by task syz-executor062/3796 [ 31.318256] [ 31.319858] CPU: 1 PID: 3796 Comm: syz-executor062 Not tainted 4.9.109-g7cecc75 #54 [ 31.327629] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 31.336957] ffff8801b6affcb0 ffffffff81eb3e29 ffffea00071f9380 ffff8801c7e4e500 [ 31.344934] 0000000000000000 ffff8801c7e4e500 ffffffff83013be0 ffff8801b6affce8 [ 31.352902] ffffffff81567a89 ffff8801c7e4e500 0000000000000004 0000000000000000 [ 31.360883] Call Trace: [ 31.363440] [] dump_stack+0xc1/0x128 [ 31.368777] [] ? sock_release+0x1c0/0x1c0 [ 31.374546] [] print_address_description+0x6c/0x234 [ 31.381182] [] ? sock_release+0x1c0/0x1c0 [ 31.387068] [] kasan_report.cold.6+0x242/0x2fe [ 31.393276] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 31.400003] [] __asan_report_load4_noabort+0x14/0x20 [ 31.406726] [] l2tp_session_queue_purge+0xf4/0x100 [ 31.413276] [] ? sock_release+0x1c0/0x1c0 [ 31.419048] [] pppol2tp_release+0x1fb/0x2e0 [ 31.424991] [] sock_release+0x96/0x1c0 [ 31.430500] [] sock_close+0x16/0x20 [ 31.435749] [] __fput+0x263/0x700 [ 31.440825] [] ____fput+0x15/0x20 [ 31.445900] [] task_work_run+0x10c/0x180 [ 31.451581] [] exit_to_usermode_loop+0xfc/0x120 [ 31.457874] [] do_syscall_64+0x364/0x490 [ 31.463556] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 31.470453] [ 31.472053] Allocated by task 3795: [ 31.475649] save_stack_trace+0x16/0x20 [ 31.479591] save_stack+0x43/0xd0 [ 31.483014] kasan_kmalloc+0xc7/0xe0 [ 31.486696] __kmalloc+0x11d/0x300 [ 31.490208] l2tp_session_create+0x38/0x16f0 [ 31.494583] pppol2tp_connect+0x10d7/0x18f0 [ 31.498876] SYSC_connect+0x1b8/0x300 [ 31.502648] SyS_connect+0x24/0x30 [ 31.506161] do_syscall_64+0x1a6/0x490 [ 31.510025] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 31.515093] [ 31.516691] Freed by task 3795: [ 31.519942] save_stack_trace+0x16/0x20 [ 31.523888] save_stack+0x43/0xd0 [ 31.527315] kasan_slab_free+0x72/0xc0 [ 31.531170] kfree+0xfb/0x310 [ 31.534243] l2tp_session_free+0x166/0x200 [ 31.538450] l2tp_tunnel_closeall+0x284/0x350 [ 31.542916] l2tp_udp_encap_destroy+0x87/0xe0 [ 31.547383] udp_destroy_sock+0x118/0x1a0 [ 31.551502] sk_common_release+0x6d/0x300 [ 31.555617] udp_lib_close+0x15/0x20 [ 31.559300] inet_release+0xff/0x1d0 [ 31.562983] sock_release+0x96/0x1c0 [ 31.566668] sock_close+0x16/0x20 [ 31.570089] __fput+0x263/0x700 [ 31.573336] ____fput+0x15/0x20 [ 31.576586] task_work_run+0x10c/0x180 [ 31.580444] exit_to_usermode_loop+0xfc/0x120 [ 31.584907] do_syscall_64+0x364/0x490 [ 31.588767] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 31.593834] [ 31.595430] The buggy address belongs to the object at ffff8801c7e4e500 [ 31.595430] which belongs to the cache kmalloc-512 of size 512 [ 31.608056] The buggy address is located 0 bytes inside of [ 31.608056] 512-byte region [ffff8801c7e4e500, ffff8801c7e4e700) [ 31.619733] The buggy address belongs to the page: [ 31.624633] page:ffffea00071f9380 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 31.634803] flags: 0x8000000000004080(slab|head) [ 31.639526] page dumped because: kasan: bad access detected [ 31.645220] [ 31.646816] Memory state around the buggy address: [ 31.651713] ffff8801c7e4e400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 31.659041] ffff8801c7e4e480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 31.666370] >ffff8801c7e4e500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 31.673708] ^ [ 31.677044] ffff8801c7e4e580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 31.684370] ffff8801c7e4e600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 31.691694] ================================================================== [ 31.699021] Disabling lock debugging due to kernel taint [ 31.704504] Kernel panic - not syncing: panic_on_warn set ... [ 31.704504] [ 31.711852] CPU: 1 PID: 3796 Comm: syz-executor062 Tainted: G B 4.9.109-g7cecc75 #54 [ 31.720832] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 31.730160] ffff8801b6affc10 ffffffff81eb3e29 ffffffff843c62e7 00000000ffffffff [ 31.738146] 0000000000000000 0000000000000001 ffffffff83013be0 ffff8801b6affcd0 [ 31.746133] ffffffff81421925 0000000041b58ab3 ffffffff843b9a00 ffffffff81421766 [ 31.754106] Call Trace: [ 31.756665] [] dump_stack+0xc1/0x128 [ 31.762001] [] ? sock_release+0x1c0/0x1c0 [ 31.767770] [] panic+0x1bf/0x3bc [ 31.772756] [] ? add_taint.cold.6+0x16/0x16 [ 31.778699] [] ? ___preempt_schedule+0x16/0x18 [ 31.784901] [] kasan_end_report+0x47/0x4f [ 31.790674] [] kasan_report.cold.6+0x76/0x2fe [ 31.796793] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 31.803515] [] __asan_report_load4_noabort+0x14/0x20 [ 31.810242] [] l2tp_session_queue_purge+0xf4/0x100 [ 31.816790] [] ? sock_release+0x1c0/0x1c0 [ 31.822554] [] pppol2tp_release+0x1fb/0x2e0 [ 31.828494] [] sock_release+0x96/0x1c0 [ 31.834001] [] sock_close+0x16/0x20 [ 31.839248] [] __fput+0x263/0x700 [ 31.844321] [] ____fput+0x15/0x20 [ 31.849397] [] task_work_run+0x10c/0x180 [ 31.855078] [] exit_to_usermode_loop+0xfc/0x120 [ 31.861365] [] do_syscall_64+0x364/0x490 [ 31.867058] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 31.874458] Dumping ftrace buffer: [ 31.877975] (ftrace buffer empty) [ 31.881658] Kernel Offset: disabled [ 31.885261] Rebooting in 86400 seconds..