[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 13.511693] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 22.596274] random: sshd: uninitialized urandom read (32 bytes read) [ 23.000934] random: sshd: uninitialized urandom read (32 bytes read) [ 23.786487] random: sshd: uninitialized urandom read (32 bytes read) [ 23.919574] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.0.42' (ECDSA) to the list of known hosts. executing program [ 29.718300] random: sshd: uninitialized urandom read (32 bytes read) [ 29.871991] ================================================================== [ 29.879684] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 29.886951] Read of size 4 at addr ffff8801ca488000 by task syz-executor057/3799 [ 29.894462] [ 29.896092] CPU: 0 PID: 3799 Comm: syz-executor057 Not tainted 4.9.113-g90e7a90 #68 [ 29.903886] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 29.913416] ffff8801d94b7cb0 ffffffff81eb4569 ffffea0007292200 ffff8801ca488000 [ 29.921470] 0000000000000000 ffff8801ca488000 ffffffff83014be0 ffff8801d94b7ce8 [ 29.929633] ffffffff81567c59 ffff8801ca488000 0000000000000004 0000000000000000 [ 29.937654] Call Trace: [ 29.940225] [] dump_stack+0xc1/0x128 [ 29.945590] [] ? sock_release+0x1c0/0x1c0 [ 29.951374] [] print_address_description+0x6c/0x234 [ 29.958044] [] ? sock_release+0x1c0/0x1c0 [ 29.963830] [] kasan_report.cold.6+0x242/0x2fe [ 29.970089] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 29.976834] [] __asan_report_load4_noabort+0x14/0x20 [ 29.983583] [] l2tp_session_queue_purge+0xf4/0x100 [ 29.990154] [] ? sock_release+0x1c0/0x1c0 [ 29.996016] [] pppol2tp_release+0x1fb/0x2e0 [ 30.001985] [] sock_release+0x96/0x1c0 [ 30.007599] [] sock_close+0x16/0x20 [ 30.012858] [] __fput+0x263/0x700 [ 30.017958] [] ____fput+0x15/0x20 [ 30.023066] [] task_work_run+0x10c/0x180 [ 30.028775] [] exit_to_usermode_loop+0xfc/0x120 [ 30.035083] [] do_syscall_64+0x364/0x490 [ 30.040801] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 30.047710] [ 30.049321] Allocated by task 3798: [ 30.052942] save_stack_trace+0x16/0x20 [ 30.056912] save_stack+0x43/0xd0 [ 30.060339] kasan_kmalloc+0xc7/0xe0 [ 30.064042] __kmalloc+0x11d/0x300 [ 30.068267] l2tp_session_create+0x38/0x16f0 [ 30.072667] pppol2tp_connect+0x10d7/0x18f0 [ 30.077494] SYSC_connect+0x1b8/0x300 [ 30.081285] SyS_connect+0x24/0x30 [ 30.084811] do_syscall_64+0x1a6/0x490 [ 30.088690] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 30.093768] [ 30.095377] Freed by task 3798: [ 30.098640] save_stack_trace+0x16/0x20 [ 30.102595] save_stack+0x43/0xd0 [ 30.106042] kasan_slab_free+0x72/0xc0 [ 30.109910] kfree+0xfb/0x310 [ 30.112997] l2tp_session_free+0x166/0x200 [ 30.117212] l2tp_tunnel_closeall+0x284/0x350 [ 30.121687] l2tp_udp_encap_destroy+0x87/0xe0 [ 30.126176] udpv6_destroy_sock+0xb1/0xd0 [ 30.130317] sk_common_release+0x6d/0x300 [ 30.134462] udp_lib_close+0x15/0x20 [ 30.138158] inet_release+0xff/0x1d0 [ 30.141851] inet6_release+0x50/0x70 [ 30.145569] sock_release+0x96/0x1c0 [ 30.149262] sock_close+0x16/0x20 [ 30.152694] __fput+0x263/0x700 [ 30.156003] ____fput+0x15/0x20 [ 30.159264] task_work_run+0x10c/0x180 [ 30.163577] exit_to_usermode_loop+0xfc/0x120 [ 30.168157] do_syscall_64+0x364/0x490 [ 30.172032] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 30.177114] [ 30.178794] The buggy address belongs to the object at ffff8801ca488000 [ 30.178794] which belongs to the cache kmalloc-512 of size 512 [ 30.191454] The buggy address is located 0 bytes inside of [ 30.191454] 512-byte region [ffff8801ca488000, ffff8801ca488200) [ 30.203133] The buggy address belongs to the page: [ 30.208059] page:ffffea0007292200 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 30.218261] flags: 0x8000000000004080(slab|head) [ 30.222991] page dumped because: kasan: bad access detected [ 30.228676] [ 30.230298] Memory state around the buggy address: [ 30.235218] ffff8801ca487f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 30.242706] ffff8801ca487f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 30.250081] >ffff8801ca488000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 30.257418] ^ [ 30.260776] ffff8801ca488080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 30.268130] ffff8801ca488100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 30.275556] ================================================================== [ 30.282903] Disabling lock debugging due to kernel taint [ 30.288950] Kernel panic - not syncing: panic_on_warn set ... [ 30.288950] [ 30.296417] CPU: 0 PID: 3799 Comm: syz-executor057 Tainted: G B 4.9.113-g90e7a90 #68 [ 30.305407] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 30.314839] ffff8801d94b7c10 ffffffff81eb4569 ffffffff843c87af 00000000ffffffff [ 30.322845] 0000000000000000 0000000000000000 ffffffff83014be0 ffff8801d94b7cd0 [ 30.330985] ffffffff81421a55 0000000041b58ab3 ffffffff843bbec8 ffffffff81421896 [ 30.339031] Call Trace: [ 30.341601] [] dump_stack+0xc1/0x128 [ 30.346970] [] ? sock_release+0x1c0/0x1c0 [ 30.352759] [] panic+0x1bf/0x3bc [ 30.357764] [] ? add_taint.cold.6+0x16/0x16 [ 30.363731] [] ? ___preempt_schedule+0x16/0x18 [ 30.369961] [] kasan_end_report+0x47/0x4f [ 30.375751] [] kasan_report.cold.6+0x76/0x2fe [ 30.381895] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 30.388822] [] __asan_report_load4_noabort+0x14/0x20 [ 30.395579] [] l2tp_session_queue_purge+0xf4/0x100 [ 30.402231] [] ? sock_release+0x1c0/0x1c0 [ 30.408031] [] pppol2tp_release+0x1fb/0x2e0 [ 30.414027] [] sock_release+0x96/0x1c0 [ 30.419549] [] sock_close+0x16/0x20 [ 30.424810] [] __fput+0x263/0x700 [ 30.429911] [] ____fput+0x15/0x20 [ 30.435525] [] task_work_run+0x10c/0x180 [ 30.441320] [] exit_to_usermode_loop+0xfc/0x120 [ 30.447639] [] do_syscall_64+0x364/0x490 [ 30.453349] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 30.460945] Dumping ftrace buffer: [ 30.464479] (ftrace buffer empty) [ 30.468182] Kernel Offset: disabled [ 30.471803] Rebooting in 86400 seconds..