bisecting fixing commit since 59456c9cc40c8f75b5a7efa0fe1f211d9c6fcaf1 building syzkaller on 2489ab887a86e8b1b253aef742e365a606db3a4f testing commit 59456c9cc40c8f75b5a7efa0fe1f211d9c6fcaf1 compiler: gcc version 8.4.1 20210217 (GCC) kernel signature: 6bcc00cef2eed2cc77015e97707c941c46e110f43af59b006fdda3edf3083b09 run #0: crashed: KASAN: use-after-free Read in tipc_udp_xmit run #1: crashed: KASAN: use-after-free Read in tipc_udp_xmit run #2: crashed: KASAN: use-after-free Read in tipc_udp_xmit run #3: crashed: KASAN: use-after-free Read in tipc_udp_xmit run #4: OK run #5: OK run #6: OK run #7: OK run #8: OK run #9: OK run #10: OK run #11: OK run #12: OK run #13: OK run #14: OK run #15: OK run #16: OK run #17: OK run #18: OK run #19: OK reproducer seems to be flaky testing current HEAD c2276d585654e8d573366c29c565043ec36adf63 testing commit c2276d585654e8d573366c29c565043ec36adf63 compiler: gcc version 8.4.1 20210217 (GCC) kernel signature: 637e05cc302056e3099d9b2cacb972a7d0e11e8b66f2d7304c5be09a8be1cd79 run #0: crashed: KASAN: use-after-free Read in tipc_udp_xmit run #1: crashed: KASAN: use-after-free Read in tipc_udp_xmit run #2: crashed: KASAN: use-after-free Read in tipc_udp_xmit run #3: crashed: KASAN: use-after-free Read in tipc_udp_xmit run #4: OK run #5: OK run #6: OK run #7: OK run #8: OK run #9: OK run #10: OK run #11: OK run #12: OK run #13: OK run #14: OK run #15: OK run #16: OK run #17: OK run #18: OK run #19: OK Reproducer flagged being flaky revisions tested: 2, total time: 42m20.69738201s (build: 17m43.921448252s, test: 24m8.891245484s) the crash still happens on HEAD commit msg: Linux 4.19.208 crash: KASAN: use-after-free Read in tipc_udp_xmit Disabling bearer New replicast peer: fe80:0000:0000:0000:0000:0000:0000:0000 Enabled bearer , priority 10 Disabling bearer ================================================================== BUG: KASAN: use-after-free in tipc_udp_xmit.isra.3+0x9de/0xc70 net/tipc/udp_media.c:200 Read of size 8 at addr ffff88807ad7e160 by task syz-executor.3/3779 CPU: 1 PID: 3779 Comm: syz-executor.3 Not tainted 4.19.208-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x17c/0x226 lib/dump_stack.c:118 print_address_description.cold.6+0x9/0x211 mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report mm/kasan/report.c:412 [inline] kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:396 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433 tipc_udp_xmit.isra.3+0x9de/0xc70 net/tipc/udp_media.c:200 tipc_udp_send_msg+0x21a/0x3c0 net/tipc/udp_media.c:248 tipc_bearer_xmit_skb+0x116/0x2a0 net/tipc/bearer.c:518 tipc_disc_timeout+0x6b6/0xa60 net/tipc/discover.c:332 call_timer_fn+0x14c/0x510 kernel/time/timer.c:1338 expire_timers+0x255/0x3a0 kernel/time/timer.c:1375 __run_timers kernel/time/timer.c:1696 [inline] run_timer_softirq+0x1dc/0x570 kernel/time/timer.c:1709 __do_softirq+0x25f/0x919 kernel/softirq.c:292 invoke_softirq kernel/softirq.c:372 [inline] irq_exit+0x17f/0x1c0 kernel/softirq.c:412 exiting_irq arch/x86/include/asm/apic.h:536 [inline] smp_apic_timer_interrupt+0x13e/0x540 arch/x86/kernel/apic/apic.c:1098 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:894 RIP: 0010:preempt_count_add+0x5c/0x1b0 kernel/sched/core.c:3238 Code: 08 84 d2 0f 85 52 01 00 00 8b 0d 7f 3f 71 0a 85 c9 75 07 65 8b 05 a4 87 c5 7e 48 b8 00 00 00 00 00 fc ff df 48 89 da 83 e3 07 <48> c1 ea 03 83 c3 03 65 44 01 25 85 87 c5 7e 0f b6 04 02 38 c3 7c RSP: 0000:ffff8880917b7b08 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13 RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: ffffffff8bad9720 RSI: 0000000000000004 RDI: 0000000000000001 RBP: ffff8880917b7b18 R08: ffffed101746455b R09: ffffed101746455a R10: ffffed101746455a R11: ffff8880ba322ad3 R12: 0000000000000001 R13: ffff8880917b7c90 R14: ffff8880b12d8840 R15: ffffffff8818c080 rcu_lockdep_current_cpu_online+0x47/0x1d0 kernel/rcu/tree.c:1076 rcu_read_lock_held+0x90/0xc0 kernel/rcu/update.c:285 radix_tree_deref_slot include/linux/radix-tree.h:241 [inline] filemap_map_pages+0xa10/0xeb0 mm/filemap.c:2652 do_fault_around mm/memory.c:3776 [inline] do_read_fault mm/memory.c:3810 [inline] do_fault mm/memory.c:3944 [inline] handle_pte_fault mm/memory.c:4175 [inline] __handle_mm_fault+0x2398/0x4100 mm/memory.c:4299 handle_mm_fault+0x3dd/0x8b0 mm/memory.c:4336 __do_page_fault+0x4dc/0xab0 arch/x86/mm/fault.c:1412 do_page_fault+0x64/0x3b0 arch/x86/mm/fault.c:1487 page_fault+0x1e/0x30 arch/x86/entry/entry_64.S:1205 RIP: 0033:0x4363a0 Code: Bad RIP value. RSP: 002b:00007ffead4e0af8 EFLAGS: 00010206 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 000000000041a483 RDX: 0000000000000000 RSI: 0000000000000018 RDI: 00000000027366e0 RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000002736400 R10: 00000000027366d0 R11: 0000000000000202 R12: 0000000000000001 R13: 0000000000000000 R14: 0000000000000001 R15: 00007ffead4e0bf0 Allocated by task 3758: save_stack mm/kasan/kasan.c:448 [inline] set_track mm/kasan/kasan.c:460 [inline] kasan_kmalloc.part.1+0x62/0xf0 mm/kasan/kasan.c:553 kasan_kmalloc+0xaf/0xc0 mm/kasan/kasan.c:538 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490 kmem_cache_alloc+0x12e/0x390 mm/slab.c:3559 sock_alloc_inode+0x18/0x230 net/socket.c:244 alloc_inode+0x56/0x150 fs/inode.c:211 new_inode_pseudo+0xc/0xd0 fs/inode.c:911 sock_alloc+0x3c/0x270 net/socket.c:567 __sock_create+0x7a/0x540 net/socket.c:1329 sock_create_kern+0xf/0x20 net/socket.c:1434 udp_sock_create6+0xe2/0x500 net/ipv6/ip6_udp_tunnel.c:22 udp_sock_create include/net/udp_tunnel.h:61 [inline] tipc_udp_enable+0x91f/0x1100 net/tipc/udp_media.c:734 tipc_enable_bearer+0x4d9/0x9e0 net/tipc/bearer.c:317 __tipc_nl_bearer_enable+0x293/0x3f0 net/tipc/bearer.c:916 tipc_nl_bearer_enable+0x1d/0x30 net/tipc/bearer.c:925 genl_family_rcv_msg+0x599/0x1000 net/netlink/genetlink.c:602 genl_rcv_msg+0xa7/0x140 net/netlink/genetlink.c:627 netlink_rcv_skb+0x13e/0x3d0 net/netlink/af_netlink.c:2457 genl_rcv+0x23/0x40 net/netlink/genetlink.c:638 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline] netlink_unicast+0x443/0x660 net/netlink/af_netlink.c:1346 netlink_sendmsg+0x667/0xc60 net/netlink/af_netlink.c:1911 sock_sendmsg_nosec net/socket.c:651 [inline] sock_sendmsg+0xac/0xf0 net/socket.c:661 ___sys_sendmsg+0x647/0x950 net/socket.c:2227 __sys_sendmsg+0xd9/0x180 net/socket.c:2265 __do_sys_sendmsg net/socket.c:2274 [inline] __se_sys_sendmsg net/socket.c:2272 [inline] __x64_sys_sendmsg+0x73/0xb0 net/socket.c:2272 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe Freed by task 4709: save_stack mm/kasan/kasan.c:448 [inline] set_track mm/kasan/kasan.c:460 [inline] __kasan_slab_free+0x13c/0x220 mm/kasan/kasan.c:521 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528 __cache_free mm/slab.c:3503 [inline] kmem_cache_free+0x83/0x290 mm/slab.c:3765 sock_destroy_inode+0x4b/0x60 net/socket.c:272 destroy_inode+0xb3/0x100 fs/inode.c:268 evict+0x36f/0x590 fs/inode.c:576 iput_final fs/inode.c:1555 [inline] iput fs/inode.c:1581 [inline] iput+0x378/0x6b0 fs/inode.c:1567 __sock_release+0x205/0x290 net/socket.c:611 sock_release+0xb/0x10 net/socket.c:619 udp_tunnel_sock_release+0x69/0x80 net/ipv4/udp_tunnel.c:190 cleanup_bearer+0x179/0x250 net/tipc/udp_media.c:775 process_one_work+0x7b9/0x15a0 kernel/workqueue.c:2153 worker_thread+0x85/0xb60 kernel/workqueue.c:2296 kthread+0x347/0x410 kernel/kthread.c:259 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415 The buggy address belongs to the object at ffff88807ad7e140 which belongs to the cache sock_inode_cache of size 992 The buggy address is located 32 bytes inside of 992-byte region [ffff88807ad7e140, ffff88807ad7e520) The buggy address belongs to the page: page:ffffea0001eb5f80 count:1 mapcount:0 mapping:ffff8880b5baed80 index:0xffff88807ad7effd flags: 0xfff00000000100(slab) raw: 00fff00000000100 ffffea0001eb5f48 ffffea0001eb5fc8 ffff8880b5baed80 raw: ffff88807ad7effd ffff88807ad7e140 0000000100000003 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff88807ad7e000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff88807ad7e080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff88807ad7e100: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb ^ ffff88807ad7e180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff88807ad7e200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== ---------------- Code disassembly (best guess): 0: 08 84 d2 0f 85 52 01 or %al,0x152850f(%rdx,%rdx,8) 7: 00 00 add %al,(%rax) 9: 8b 0d 7f 3f 71 0a mov 0xa713f7f(%rip),%ecx # 0xa713f8e f: 85 c9 test %ecx,%ecx 11: 75 07 jne 0x1a 13: 65 8b 05 a4 87 c5 7e mov %gs:0x7ec587a4(%rip),%eax # 0x7ec587be 1a: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax 21: fc ff df 24: 48 89 da mov %rbx,%rdx 27: 83 e3 07 and $0x7,%ebx * 2a: 48 c1 ea 03 shr $0x3,%rdx <-- trapping instruction 2e: 83 c3 03 add $0x3,%ebx 31: 65 44 01 25 85 87 c5 add %r12d,%gs:0x7ec58785(%rip) # 0x7ec587be 38: 7e 39: 0f b6 04 02 movzbl (%rdx,%rax,1),%eax 3d: 38 c3 cmp %al,%bl 3f: 7c .byte 0x7c