[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[ 14.362851] random: sshd: uninitialized urandom read (32 bytes read) [?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 syzkaller login: [ 21.524102] random: sshd: uninitialized urandom read (32 bytes read) [ 22.128042] random: sshd: uninitialized urandom read (32 bytes read) [ 22.969024] random: sshd: uninitialized urandom read (32 bytes read) [ 23.092259] random: sshd: uninitialized urandom read (32 bytes read) Warning: Permanently added '10.128.0.40' (ECDSA) to the list of known hosts. [ 28.551584] random: sshd: uninitialized urandom read (32 bytes read) executing program [ 28.736041] ================================================================== [ 28.743432] BUG: KASAN: use-after-free in l2tp_session_queue_purge+0xf4/0x100 [ 28.750679] Read of size 4 at addr ffff8801c9e21400 by task syz-executor507/3799 [ 28.758180] [ 28.759779] CPU: 1 PID: 3799 Comm: syz-executor507 Not tainted 4.9.104-g135beb9 #40 [ 28.767548] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 28.776874] ffff8801da37fcb0 ffffffff81eb44c9 ffffea0007278800 ffff8801c9e21400 [ 28.784847] 0000000000000000 ffff8801c9e21400 ffffffff83013be0 ffff8801da37fce8 [ 28.792822] ffffffff81567e49 ffff8801c9e21400 0000000000000004 0000000000000000 [ 28.800794] Call Trace: [ 28.803352] [] dump_stack+0xc1/0x128 [ 28.808693] [] ? sock_release+0x1c0/0x1c0 [ 28.814465] [] print_address_description+0x6c/0x234 [ 28.821103] [] ? sock_release+0x1c0/0x1c0 [ 28.826871] [] kasan_report.cold.6+0x242/0x2fe [ 28.833072] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 28.839792] [] __asan_report_load4_noabort+0x14/0x20 [ 28.846515] [] l2tp_session_queue_purge+0xf4/0x100 [ 28.853064] [] ? sock_release+0x1c0/0x1c0 [ 28.858829] [] pppol2tp_release+0x1fb/0x2e0 [ 28.864778] [] sock_release+0x96/0x1c0 [ 28.870284] [] sock_close+0x16/0x20 [ 28.875537] [] __fput+0x263/0x700 [ 28.880613] [] ____fput+0x15/0x20 [ 28.885689] [] task_work_run+0x10c/0x180 [ 28.891372] [] exit_to_usermode_loop+0xfc/0x120 [ 28.897660] [] do_syscall_64+0x364/0x490 [ 28.903360] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 28.910254] [ 28.911854] Allocated by task 3801: [ 28.915454] save_stack_trace+0x16/0x20 [ 28.919399] save_stack+0x43/0xd0 [ 28.922818] kasan_kmalloc+0xc7/0xe0 [ 28.926500] __kmalloc+0x11d/0x300 [ 28.930014] l2tp_session_create+0x38/0x16f0 [ 28.934390] pppol2tp_connect+0x10d7/0x18f0 [ 28.938682] SYSC_connect+0x1b8/0x300 [ 28.942450] SyS_connect+0x24/0x30 [ 28.945961] do_syscall_64+0x1a6/0x490 [ 28.949827] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 28.954894] [ 28.956491] Freed by task 3801: [ 28.959741] save_stack_trace+0x16/0x20 [ 28.963682] save_stack+0x43/0xd0 [ 28.967102] kasan_slab_free+0x72/0xc0 [ 28.970957] kfree+0xfb/0x310 [ 28.974035] l2tp_session_free+0x166/0x200 [ 28.978240] l2tp_tunnel_closeall+0x284/0x350 [ 28.982705] l2tp_udp_encap_destroy+0x87/0xe0 [ 28.987172] udp_destroy_sock+0x118/0x1a0 [ 28.991288] sk_common_release+0x6d/0x300 [ 28.995405] udp_lib_close+0x15/0x20 [ 28.999088] inet_release+0xff/0x1d0 [ 29.002770] sock_release+0x96/0x1c0 [ 29.006453] sock_close+0x16/0x20 [ 29.009878] __fput+0x263/0x700 [ 29.013126] ____fput+0x15/0x20 [ 29.016380] task_work_run+0x10c/0x180 [ 29.020240] exit_to_usermode_loop+0xfc/0x120 [ 29.024702] do_syscall_64+0x364/0x490 [ 29.028557] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 29.033627] [ 29.035225] The buggy address belongs to the object at ffff8801c9e21400 [ 29.035225] which belongs to the cache kmalloc-512 of size 512 [ 29.047850] The buggy address is located 0 bytes inside of [ 29.047850] 512-byte region [ffff8801c9e21400, ffff8801c9e21600) [ 29.059519] The buggy address belongs to the page: [ 29.064419] page:ffffea0007278800 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0 [ 29.074599] flags: 0x8000000000004080(slab|head) [ 29.079322] page dumped because: kasan: bad access detected [ 29.085005] [ 29.086603] Memory state around the buggy address: [ 29.091502] ffff8801c9e21300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 29.098828] ffff8801c9e21380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc [ 29.106157] >ffff8801c9e21400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 29.113483] ^ [ 29.116819] ffff8801c9e21480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 29.124158] ffff8801c9e21500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 29.131483] ================================================================== [ 29.138810] Disabling lock debugging due to kernel taint [ 29.144767] Kernel panic - not syncing: panic_on_warn set ... [ 29.144767] [ 29.152121] CPU: 1 PID: 3799 Comm: syz-executor507 Tainted: G B 4.9.104-g135beb9 #40 [ 29.161100] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 29.170427] ffff8801da37fc10 ffffffff81eb44c9 ffffffff843c6255 00000000ffffffff [ 29.178407] 0000000000000000 0000000000000001 ffffffff83013be0 ffff8801da37fcd0 [ 29.186378] ffffffff81421e15 0000000041b58ab3 ffffffff843b9988 ffffffff81421c56 [ 29.194348] Call Trace: [ 29.196911] [] dump_stack+0xc1/0x128 [ 29.202250] [] ? sock_release+0x1c0/0x1c0 [ 29.208016] [] panic+0x1bf/0x3bc [ 29.213003] [] ? add_taint.cold.6+0x16/0x16 [ 29.218948] [] ? ___preempt_schedule+0x16/0x18 [ 29.225157] [] kasan_end_report+0x47/0x4f [ 29.230925] [] kasan_report.cold.6+0x76/0x2fe [ 29.237043] [] ? l2tp_session_queue_purge+0xf4/0x100 [ 29.243775] [] __asan_report_load4_noabort+0x14/0x20 [ 29.250501] [] l2tp_session_queue_purge+0xf4/0x100 [ 29.257052] [] ? sock_release+0x1c0/0x1c0 [ 29.262822] [] pppol2tp_release+0x1fb/0x2e0 [ 29.268764] [] sock_release+0x96/0x1c0 [ 29.274272] [] sock_close+0x16/0x20 [ 29.279519] [] __fput+0x263/0x700 [ 29.284590] [] ____fput+0x15/0x20 [ 29.289671] [] task_work_run+0x10c/0x180 [ 29.295352] [] exit_to_usermode_loop+0xfc/0x120 [ 29.301638] [] do_syscall_64+0x364/0x490 [ 29.307334] [] entry_SYSCALL_64_after_swapgs+0x5d/0xdb [ 29.314690] Dumping ftrace buffer: [ 29.318202] (ftrace buffer empty) [ 29.321889] Kernel Offset: disabled [ 29.325491] Rebooting in 86400 seconds..