[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 14.316644] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 23.862351] random: sshd: uninitialized urandom read (32 bytes read) [ 24.363194] random: sshd: uninitialized urandom read (32 bytes read) [ 24.926851] random: sshd: uninitialized urandom read (32 bytes read) [ 25.054191] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.10.34' (ECDSA) to the list of known hosts. [ 30.422345] random: sshd: uninitialized urandom read (32 bytes read) executing program [ 30.580364] ================================================================== [ 30.587752] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 30.594995] Read of size 4 at addr ffff8801b881bb80 by task syz-executor175/3797 [ 30.602493] [ 30.604093] CPU: 0 PID: 3797 Comm: syz-executor175 Not tainted 4.9.96-g71fce1e #10 [ 30.611765] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 30.621093] ffff8801d920fcb0 ffffffff81eb0b69 ffffea0006e20680 ffff8801b881bb80 [ 30.629060] 0000000000000000 ffff8801b881bb80 ffffffff8300ebe0 ffff8801d920fce8 [ 30.637071] ffffffff8156540b ffff8801b881bb80 0000000000000004 0000000000000000 [ 30.645041] Call Trace: [ 30.647599] [] dump_stack+0xc1/0x128 [ 30.652932] [] ? sock_release+0x1c0/0x1c0 [ 30.658701] [] print_address_description+0x6c/0x234 [ 30.665339] [] ? sock_release+0x1c0/0x1c0 [ 30.671105] [] kasan_report.cold.6+0x242/0x2fe [ 30.677305] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 30.684029] [] __asan_report_load4_noabort+0x14/0x20 [ 30.690752] [] l2tp_session_queue_purge+0xf4/0x100 [ 30.697298] [] ? sock_release+0x1c0/0x1c0 [ 30.703066] [] pppol2tp_release+0x1fb/0x2e0 [ 30.709004] [] sock_release+0x96/0x1c0 [ 30.714510] [] sock_close+0x16/0x20 [ 30.719760] [] __fput+0x263/0x700 [ 30.724833] [] ____fput+0x15/0x20 [ 30.729905] [] task_work_run+0x10c/0x180 [ 30.735593] [] exit_to_usermode_loop+0xfc/0x120 [ 30.741881] [] do_syscall_64+0x364/0x490 [ 30.747561] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 30.754452] [ 30.756047] Allocated by task 3796: [ 30.759644] save_stack_trace+0x16/0x20 [ 30.763585] save_stack+0x43/0xd0 [ 30.767007] kasan_kmalloc+0xc7/0xe0 [ 30.770689] __kmalloc+0x11d/0x300 [ 30.774201] l2tp_session_create+0x38/0x16f0 [ 30.778575] pppol2tp_connect+0x10c5/0x18e0 [ 30.782867] SYSC_connect+0x1b8/0x300 [ 30.786633] SyS_connect+0x24/0x30 [ 30.790146] do_syscall_64+0x1a6/0x490 [ 30.794002] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 30.799070] [ 30.800666] Freed by task 3796: [ 30.803913] save_stack_trace+0x16/0x20 [ 30.807866] save_stack+0x43/0xd0 [ 30.811288] kasan_slab_free+0x72/0xc0 [ 30.815149] kfree+0xfb/0x310 [ 30.818224] l2tp_session_free+0x166/0x200 [ 30.822425] l2tp_tunnel_closeall+0x284/0x350 [ 30.826889] l2tp_udp_encap_destroy+0x87/0xe0 [ 30.831351] udpv6_destroy_sock+0xb1/0xd0 [ 30.835472] sk_common_release+0x6d/0x300 [ 30.839585] udp_lib_close+0x15/0x20 [ 30.843267] inet_release+0xff/0x1d0 [ 30.846949] inet6_release+0x50/0x70 [ 30.850630] sock_release+0x96/0x1c0 [ 30.854311] sock_close+0x16/0x20 [ 30.857735] __fput+0x263/0x700 [ 30.860981] ____fput+0x15/0x20 [ 30.864230] task_work_run+0x10c/0x180 [ 30.868085] exit_to_usermode_loop+0xfc/0x120 [ 30.872546] do_syscall_64+0x364/0x490 [ 30.876402] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 30.881475] [ 30.883073] The buggy address belongs to the object at ffff8801b881bb80 [ 30.883073] which belongs to the cache kmalloc-512 of size 512 [ 30.895699] The buggy address is located 0 bytes inside of [ 30.895699] 512-byte region [ffff8801b881bb80, ffff8801b881bd80) [ 30.907370] The buggy address belongs to the page: [ 30.912269] page:ffffea0006e20680 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 30.922432] flags: 0x8000000000004080(slab|head) [ 30.927153] page dumped because: kasan: bad access detected [ 30.932827] [ 30.934421] Memory state around the buggy address: [ 30.939319] ffff8801b881ba80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 30.946645] ffff8801b881bb00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 30.953973] >ffff8801b881bb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 30.961298] ^ [ 30.964634] ffff8801b881bc00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 30.971959] ffff8801b881bc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 30.979284] ================================================================== [ 30.986609] Disabling lock debugging due to kernel taint [ 30.992600] Kernel panic - not syncing: panic_on_warn set ... [ 30.992600] [ 30.999955] CPU: 0 PID: 3797 Comm: syz-executor175 Tainted: G B 4.9.96-g71fce1e #10 [ 31.008851] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 31.018177] ffff8801d920fc10 ffffffff81eb0b69 ffffffff841c492d 00000000ffffffff [ 31.026152] 0000000000000000 0000000000000000 ffffffff8300ebe0 ffff8801d920fcd0 [ 31.034127] ffffffff8141f975 0000000041b58ab3 ffffffff841b8030 ffffffff8141f7b6 [ 31.042104] Call Trace: [ 31.044664] [] dump_stack+0xc1/0x128 [ 31.050000] [] ? sock_release+0x1c0/0x1c0 [ 31.055776] [] panic+0x1bf/0x3bc [ 31.060762] [] ? add_taint.cold.6+0x16/0x16 [ 31.066701] [] ? ___preempt_schedule+0x16/0x18 [ 31.072903] [] kasan_end_report+0x47/0x4f [ 31.078672] [] kasan_report.cold.6+0x76/0x2fe [ 31.084789] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 31.091521] [] __asan_report_load4_noabort+0x14/0x20 [ 31.098241] [] l2tp_session_queue_purge+0xf4/0x100 [ 31.104788] [] ? sock_release+0x1c0/0x1c0 [ 31.110556] [] pppol2tp_release+0x1fb/0x2e0 [ 31.116502] [] sock_release+0x96/0x1c0 [ 31.122009] [] sock_close+0x16/0x20 [ 31.127253] [] __fput+0x263/0x700 [ 31.132323] [] ____fput+0x15/0x20 [ 31.137400] [] task_work_run+0x10c/0x180 [ 31.143079] [] exit_to_usermode_loop+0xfc/0x120 [ 31.149365] [] do_syscall_64+0x364/0x490 [ 31.155044] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 31.162431] Dumping ftrace buffer: [ 31.165942] (ftrace buffer empty) [ 31.169622] Kernel Offset: disabled [ 31.173218] Rebooting in 86400 seconds..