================================================================== BUG: KASAN: use-after-free in pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476 Read of size 4 at addr ffff8801d0e98f00 by task syzkaller717112/3336 CPU: 1 PID: 3336 Comm: syzkaller717112 Not tainted 4.4.112-g3fc4284 #32 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 0000000000000000 27f87a603c5d43e7 ffff8801d07ffc70 ffffffff81d054ed ffffea000743a600 ffff8801d0e98f00 0000000000000000 ffff8801d0e98f00 ffffffff82dea4d0 ffff8801d07ffca8 ffffffff814fd953 ffff8801d0e98f00 Call Trace: [] __dump_stack lib/dump_stack.c:15 [inline] [] dump_stack+0xc1/0x124 lib/dump_stack.c:51 [] print_address_description+0x73/0x260 mm/kasan/report.c:252 [] kasan_report_error mm/kasan/report.c:351 [inline] [] kasan_report+0x285/0x370 mm/kasan/report.c:408 [] __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:428 [] pppol2tp_session_destruct+0xee/0x110 net/l2tp/l2tp_ppp.c:476 [] sk_destruct+0x4a/0x4c0 net/core/sock.c:1447 [] __sk_free+0x57/0x230 net/core/sock.c:1480 [] sk_free+0x30/0x40 net/core/sock.c:1491 [] sock_put include/net/sock.h:1639 [inline] [] pppol2tp_release+0x27a/0x310 net/l2tp/l2tp_ppp.c:518 [] sock_release+0x8d/0x1e0 net/socket.c:586 [] sock_close+0x16/0x20 net/socket.c:1037 [] __fput+0x233/0x6d0 fs/file_table.c:208 [] ____fput+0x15/0x20 fs/file_table.c:244 [] task_work_run+0x104/0x180 kernel/task_work.c:115 [] tracehook_notify_resume include/linux/tracehook.h:191 [inline] [] exit_to_usermode_loop+0x145/0x170 arch/x86/entry/common.c:251 [] prepare_exit_to_usermode arch/x86/entry/common.c:282 [inline] [] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:347 [] int_ret_from_sys_call+0x25/0xa3 Allocated by task 3335: [] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63 [] save_stack+0x43/0xd0 mm/kasan/kasan.c:512 [] set_track mm/kasan/kasan.c:524 [inline] [] kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616 [] __kmalloc+0x124/0x320 mm/slub.c:3613 [] kmalloc include/linux/slab.h:481 [inline] [] kzalloc include/linux/slab.h:620 [inline] [] l2tp_session_create+0x39/0x10f0 net/l2tp/l2tp_core.c:1744 [] pppol2tp_connect+0x10fc/0x1930 net/l2tp/l2tp_ppp.c:718 [] SYSC_connect+0x1b6/0x310 net/socket.c:1557 [] SyS_connect+0x24/0x30 net/socket.c:1538 [] entry_SYSCALL_64_fastpath+0x16/0x92 Freed by task 3335: [] save_stack_trace+0x26/0x50 arch/x86/kernel/stacktrace.c:63 [] save_stack+0x43/0xd0 mm/kasan/kasan.c:512 [] set_track mm/kasan/kasan.c:524 [inline] [] kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:589 [] slab_free_hook mm/slub.c:1383 [inline] [] slab_free_freelist_hook mm/slub.c:1405 [inline] [] slab_free mm/slub.c:2859 [inline] [] kfree+0xfc/0x300 mm/slub.c:3749 [] l2tp_session_free+0x170/0x200 net/l2tp/l2tp_core.c:1672 [] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:293 [inline] [] l2tp_tunnel_closeall+0x2d1/0x3b0 net/l2tp/l2tp_core.c:1279 [] l2tp_udp_encap_destroy+0x8b/0xf0 net/l2tp/l2tp_core.c:1300 [] udpv6_destroy_sock+0xb1/0xd0 net/ipv6/udp.c:1421 [] sk_common_release+0x6b/0x300 net/core/sock.c:2680 [] udp_lib_close+0x15/0x20 include/net/udp.h:190 [] inet_release+0xfa/0x1d0 net/ipv4/af_inet.c:435 [] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:424 [] sock_release+0x8d/0x1e0 net/socket.c:586 [] sock_close+0x16/0x20 net/socket.c:1037 [] __fput+0x233/0x6d0 fs/file_table.c:208 [] ____fput+0x15/0x20 fs/file_table.c:244 [] task_work_run+0x104/0x180 kernel/task_work.c:115 [] tracehook_notify_resume include/linux/tracehook.h:191 [inline] [] exit_to_usermode_loop+0x145/0x170 arch/x86/entry/common.c:251 [] prepare_exit_to_usermode arch/x86/entry/common.c:282 [inline] [] syscall_return_slowpath+0x1b5/0x1f0 arch/x86/entry/common.c:347 [] int_ret_from_sys_call+0x25/0xa3 The buggy address belongs to the object at ffff8801d0e98f00 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 0 bytes inside of 512-byte region [ffff8801d0e98f00, ffff8801d0e99100) The buggy address belongs to the page: PANIC: double fault, error_code: 0x0 CPU: 1 PID: 3336 Comm: syzkaller717112 Not tainted 4.4.112-g3fc4284 #32 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 task: ffff8800b428df00 task.stack: ffff8801d07f8000 RIP: 0010:[] [] dump_page_badflags+0x8/0x250 mm/debug.c:84 RSP: 0018:ffff880100000000 EFLAGS: 00010046 RAX: ffff8800b428df00 RBX: ffffea000743a600 RCX: ffffffff8148fea0 RDX: 0000000000000000 RSI: ffffffff838a8620 RDI: ffffea000743a600 RBP: ffff880100000010 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000002 R11: fffffbfff0ad7a1e R12: 0000000000000000 R13: ffffffff838a8620 R14: 0000000000000000 R15: 0000000000000000 FS: 00007f1673ed2700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffff8800fffffff8 CR3: 00000001d0b7c000 CR4: 0000000000160670 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Stack: Call Trace: Code: 00 e9 83 fd ff ff e8 a8 e2 06 00 e9 50 fd ff ff e8 9e e2 06 00 e9 1d fd ff ff 66 0f 1f 84 00 00 00 00 00 55 48 89 e5 41 57 41 56 <41> 55 49 89 f5 41 54 49 89 d4 53 48 89 fb 48 83 ec 08 e8 11 01