[....] Starting enhanced syslogd: rsyslogd[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 14.322992] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 16.705506] random: sshd: uninitialized urandom read (32 bytes read) [ 16.968657] random: sshd: uninitialized urandom read (32 bytes read) [ 17.474762] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.0.34' (ECDSA) to the list of known hosts. [ 23.058189] urandom_read: 1 callbacks suppressed [ 23.058192] random: sshd: uninitialized urandom read (32 bytes read) executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program executing program [ 23.659150] ================================================================== [ 23.666541] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 23.673905] Read of size 4 at addr ffff8801b5dac280 by task syz-executor023/4284 [ 23.681420] [ 23.683027] CPU: 0 PID: 4284 Comm: syz-executor023 Not tainted 4.9.118-g47b77b8 #72 [ 23.690802] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 23.700139] ffff8801b53878a8 ffffffff81eb4b89 ffffea0006d76b00 ffff8801b5dac280 [ 23.708150] 0000000000000000 ffff8801b5dac280 ffffffff83015be0 ffff8801b53878e0 [ 23.716156] ffffffff81567f29 ffff8801b5dac280 0000000000000004 0000000000000000 [ 23.724159] Call Trace: [ 23.726719] [] dump_stack+0xc1/0x128 [ 23.732064] [] ? sock_release+0x1c0/0x1c0 [ 23.737840] [] print_address_description+0x6c/0x234 [ 23.744483] [] ? sock_release+0x1c0/0x1c0 [ 23.750272] [] kasan_report.cold.6+0x242/0x2fe [ 23.756484] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 23.763214] [] __asan_report_load4_noabort+0x14/0x20 [ 23.769939] [] l2tp_session_queue_purge+0xf4/0x100 [ 23.776493] [] ? sock_release+0x1c0/0x1c0 [ 23.782268] [] pppol2tp_release+0x1fb/0x2e0 [ 23.788213] [] sock_release+0x96/0x1c0 [ 23.793721] [] sock_close+0x16/0x20 [ 23.798970] [] __fput+0x263/0x700 [ 23.804066] [] ____fput+0x15/0x20 [ 23.809156] [] task_work_run+0x10c/0x180 [ 23.814901] [] do_exit+0x9e1/0x27b0 [ 23.820165] [] ? __sigqueue_free.part.26+0x51/0x60 [ 23.826724] [] ? release_task.part.19+0x1210/0x1210 [ 23.833360] [] do_group_exit+0x111/0x340 [ 23.839054] [] get_signal+0x4cf/0x1450 [ 23.844582] [] ? signal_setup_done+0xbc/0x280 [ 23.851395] [] do_signal+0x87/0x19f0 [ 23.856754] [] ? setup_sigcontext+0x7d0/0x7d0 [ 23.862888] [] ? bad_area+0x53/0x80 [ 23.868136] [] ? __do_page_fault+0x183/0xd50 [ 23.874165] [] ? exit_to_usermode_loop+0xac/0x120 [ 23.880645] [] exit_to_usermode_loop+0xe1/0x120 [ 23.886934] [] prepare_exit_to_usermode+0xbb/0xe0 [ 23.893409] [] retint_user+0x8/0x3c [ 23.898652] [ 23.900248] Allocated by task 4281: [ 23.903845] save_stack_trace+0x16/0x20 [ 23.907787] save_stack+0x43/0xd0 [ 23.911209] kasan_kmalloc+0xc7/0xe0 [ 23.914894] __kmalloc+0x11d/0x300 [ 23.918439] l2tp_session_create+0x38/0x16f0 [ 23.922835] pppol2tp_connect+0x10d7/0x18f0 [ 23.927143] SYSC_connect+0x1b8/0x300 [ 23.930914] SyS_connect+0x24/0x30 [ 23.934425] do_syscall_64+0x1a6/0x490 [ 23.938290] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 23.943358] [ 23.944952] Freed by task 4233: [ 23.948219] save_stack_trace+0x16/0x20 [ 23.952161] save_stack+0x43/0xd0 [ 23.955584] kasan_slab_free+0x72/0xc0 [ 23.959441] kfree+0xfb/0x310 [ 23.962513] l2tp_session_free+0x166/0x200 [ 23.966721] l2tp_tunnel_closeall+0x284/0x350 [ 23.971193] l2tp_udp_encap_destroy+0x87/0xe0 [ 23.975675] udpv6_destroy_sock+0xb1/0xd0 [ 23.979797] sk_common_release+0x6d/0x300 [ 23.983915] udp_lib_close+0x15/0x20 [ 23.987607] inet_release+0xff/0x1d0 [ 23.991292] inet6_release+0x50/0x70 [ 23.994975] sock_release+0x96/0x1c0 [ 23.998668] sock_close+0x16/0x20 [ 24.002091] __fput+0x263/0x700 [ 24.005357] ____fput+0x15/0x20 [ 24.008625] task_work_run+0x10c/0x180 [ 24.012485] do_exit+0x9e1/0x27b0 [ 24.015916] do_group_exit+0x111/0x340 [ 24.019913] get_signal+0x4cf/0x1450 [ 24.023596] do_signal+0x87/0x19f0 [ 24.027106] exit_to_usermode_loop+0xe1/0x120 [ 24.031570] prepare_exit_to_usermode+0xbb/0xe0 [ 24.036225] retint_user+0x8/0x3c [ 24.039647] [ 24.041282] The buggy address belongs to the object at ffff8801b5dac280 [ 24.041282] which belongs to the cache kmalloc-512 of size 512 [ 24.054066] The buggy address is located 0 bytes inside of [ 24.054066] 512-byte region [ffff8801b5dac280, ffff8801b5dac480) [ 24.065758] The buggy address belongs to the page: [ 24.070658] page:ffffea0006d76b00 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 24.080865] flags: 0x8000000000004080(slab|head) [ 24.085635] page dumped because: kasan: bad access detected [ 24.091313] [ 24.092911] Memory state around the buggy address: [ 24.097839] ffff8801b5dac180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 24.105203] ffff8801b5dac200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 24.112549] >ffff8801b5dac280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 24.119877] ^ [ 24.123212] ffff8801b5dac300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 24.130561] ffff8801b5dac380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 24.137898] ================================================================== [ 24.145226] Disabling lock debugging due to kernel taint [ 24.151462] Kernel panic - not syncing: panic_on_warn set ... [ 24.151462] [ 24.159046] CPU: 1 PID: 4284 Comm: syz-executor023 Tainted: G B 4.9.118-g47b77b8 #72 [ 24.168062] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 24.177416] ffff8801b5387808 ffffffff81eb4b89 ffffffff843c8907 00000000ffffffff [ 24.185411] 0000000000000000 0000000000000001 ffffffff83015be0 ffff8801b53878c8 [ 24.193401] ffffffff81421c25 0000000041b58ab3 ffffffff843bbfe8 ffffffff81421a66 [ 24.201420] Call Trace: [ 24.204104] [] dump_stack+0xc1/0x128 [ 24.209556] [] ? sock_release+0x1c0/0x1c0 [ 24.215342] [] panic+0x1bf/0x3bc [ 24.220331] [] ? add_taint.cold.6+0x16/0x16 [ 24.226277] [] ? ___preempt_schedule+0x16/0x18 [ 24.232493] [] kasan_end_report+0x47/0x4f [ 24.238271] [] kasan_report.cold.6+0x76/0x2fe [ 24.244388] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 24.251111] [] __asan_report_load4_noabort+0x14/0x20 [ 24.257934] [] l2tp_session_queue_purge+0xf4/0x100 [ 24.264493] [] ? sock_release+0x1c0/0x1c0 [ 24.270272] [] pppol2tp_release+0x1fb/0x2e0 [ 24.276241] [] sock_release+0x96/0x1c0 [ 24.281748] [] sock_close+0x16/0x20 [ 24.286995] [] __fput+0x263/0x700 [ 24.292068] [] ____fput+0x15/0x20 [ 24.297145] [] task_work_run+0x10c/0x180 [ 24.302840] [] do_exit+0x9e1/0x27b0 [ 24.308108] [] ? __sigqueue_free.part.26+0x51/0x60 [ 24.314660] [] ? release_task.part.19+0x1210/0x1210 [ 24.321297] [] do_group_exit+0x111/0x340 [ 24.326992] [] get_signal+0x4cf/0x1450 [ 24.332503] [] ? signal_setup_done+0xbc/0x280 [ 24.338636] [] do_signal+0x87/0x19f0 [ 24.343971] [] ? setup_sigcontext+0x7d0/0x7d0 [ 24.350092] [] ? bad_area+0x53/0x80 [ 24.355352] [] ? __do_page_fault+0x183/0xd50 [ 24.361388] [] ? exit_to_usermode_loop+0xac/0x120 [ 24.367853] [] exit_to_usermode_loop+0xe1/0x120 [ 24.374153] [] prepare_exit_to_usermode+0xbb/0xe0 [ 24.380633] [] retint_user+0x8/0x3c [ 24.386263] Dumping ftrace buffer: [ 24.389781] (ftrace buffer empty) [ 24.393504] Kernel Offset: disabled [ 24.397106] Rebooting in 86400 seconds..