bisecting fixing commit since 2034d6f0838e465dd8f120c4e946d8444b4bb5df building syzkaller on 6a81331a1d4c744da9204d02ec88d558f7eea9c9 testing commit 2034d6f0838e465dd8f120c4e946d8444b4bb5df with gcc (GCC) 8.4.1 20210217 kernel signature: 3adb7525aedb77d026120eac61af827936cc84243d4c54febc1cb6b54102d4ba run #0: crashed: KASAN: use-after-free Read in ip_check_mc_rcu run #1: crashed: KASAN: use-after-free Read in ip_check_mc_rcu run #2: crashed: KASAN: use-after-free Read in ip_check_mc_rcu run #3: crashed: KASAN: use-after-free Read in ip_check_mc_rcu run #4: crashed: KASAN: use-after-free Read in ip_check_mc_rcu run #5: crashed: KASAN: use-after-free Read in ip_check_mc_rcu 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 6b7b0056defc6eb5c87bbe4690ccda547b2891aa testing commit 6b7b0056defc6eb5c87bbe4690ccda547b2891aa with gcc (GCC) 8.4.1 20210217 kernel signature: b3e95fbbccc564b0d5595318541efb9bad6051533c2f2c606a6d60f5c4c6e3a3 run #0: crashed: KASAN: use-after-free Read in ip_check_mc_rcu run #1: crashed: KASAN: use-after-free Read in ip_check_mc_rcu run #2: crashed: KASAN: use-after-free Read in ip_check_mc_rcu run #3: crashed: KASAN: use-after-free Read in ip_check_mc_rcu run #4: crashed: KASAN: use-after-free Read in ip_check_mc_rcu run #5: crashed: KASAN: use-after-free Read in ip_check_mc_rcu run #6: crashed: KASAN: use-after-free Read in ip_check_mc_rcu run #7: crashed: KASAN: use-after-free Read in ip_check_mc_rcu 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: 34m58.619572679s (build: 15m57.230850259s, test: 18m39.096127363s) the crash still happens on HEAD commit msg: Linux 4.19.192 crash: KASAN: use-after-free Read in ip_check_mc_rcu ================================================================== BUG: KASAN: use-after-free in ip_check_mc_rcu+0x4d4/0x530 net/ipv4/igmp.c:2738 Read of size 8 at addr ffff88809b8b9700 by task syz-executor.1/15845 CPU: 1 PID: 15845 Comm: syz-executor.1 Not tainted 4.19.192-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 ip_check_mc_rcu+0x4d4/0x530 net/ipv4/igmp.c:2738 __mkroute_output net/ipv4/route.c:2267 [inline] ip_route_output_key_hash_rcu+0x1e85/0x2ab0 net/ipv4/route.c:2547 ip_route_output_key_hash+0x18f/0x2a0 net/ipv4/route.c:2375 __ip_route_output_key include/net/route.h:124 [inline] ip_route_output_flow+0x1f/0x140 net/ipv4/route.c:2632 udp_sendmsg+0x141f/0x2120 net/ipv4/udp.c:1101 inet_sendmsg+0x108/0x440 net/ipv4/af_inet.c:798 sock_sendmsg_nosec net/socket.c:622 [inline] sock_sendmsg+0xac/0xf0 net/socket.c:632 ___sys_sendmsg+0x28e/0x950 net/socket.c:2115 __sys_sendmmsg+0x160/0x370 net/socket.c:2210 __do_sys_sendmmsg net/socket.c:2239 [inline] __se_sys_sendmmsg net/socket.c:2236 [inline] __x64_sys_sendmmsg+0x98/0x100 net/socket.c:2236 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x466459 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f6d4d475188 EFLAGS: 00000246 ORIG_RAX: 0000000000000133 RAX: ffffffffffffffda RBX: 000000000056bf60 RCX: 0000000000466459 RDX: 000000000800001d RSI: 0000000020007fc0 RDI: 0000000000000004 RBP: 00000000004bf9fb R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf60 R13: 00007ffe91b9dedf R14: 00007f6d4d475300 R15: 0000000000022000 Allocated by task 15845: 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 kmem_cache_alloc_trace+0x152/0x3a0 mm/slab.c:3625 kmalloc include/linux/slab.h:515 [inline] kzalloc include/linux/slab.h:709 [inline] ip_mc_add1_src net/ipv4/igmp.c:1986 [inline] ip_mc_add_src+0x926/0xe30 net/ipv4/igmp.c:2110 ip_mc_source+0x881/0x1000 net/ipv4/igmp.c:2431 do_ip_setsockopt.isra.4+0x16f0/0x2800 net/ipv4/ip_sockglue.c:996 ip_setsockopt+0x27/0x70 net/ipv4/ip_sockglue.c:1246 tcp_setsockopt net/ipv4/tcp.c:3108 [inline] tcp_setsockopt+0x6a/0xd0 net/ipv4/tcp.c:3102 sock_common_setsockopt+0x73/0xf0 net/core/sock.c:3072 __sys_setsockopt+0x13e/0x210 net/socket.c:1901 __do_sys_setsockopt net/socket.c:1912 [inline] __se_sys_setsockopt net/socket.c:1909 [inline] __x64_sys_setsockopt+0xb9/0x150 net/socket.c:1909 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293 entry_SYSCALL_64_after_hwframe+0x49/0xbe Freed by task 15841: 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] kfree+0xcf/0x220 mm/slab.c:3822 ip_mc_del1_src+0x52e/0x740 net/ipv4/igmp.c:1899 ip_mc_del_src+0x3d3/0x8e0 net/ipv4/igmp.c:1940 ip_mc_leave_src+0xd7/0x200 net/ipv4/igmp.c:2246 ip_mc_drop_socket+0x10d/0x210 net/ipv4/igmp.c:2700 inet_release+0x47/0x1b0 net/ipv4/af_inet.c:414 __sock_release+0xc2/0x290 net/socket.c:579 sock_close+0x10/0x20 net/socket.c:1140 __fput+0x249/0x7f0 fs/file_table.c:278 ____fput+0x9/0x10 fs/file_table.c:309 task_work_run+0x108/0x180 kernel/task_work.c:113 tracehook_notify_resume include/linux/tracehook.h:193 [inline] exit_to_usermode_loop+0x185/0x1e0 arch/x86/entry/common.c:167 prepare_exit_to_usermode arch/x86/entry/common.c:198 [inline] syscall_return_slowpath arch/x86/entry/common.c:271 [inline] do_syscall_64+0x413/0x4e0 arch/x86/entry/common.c:296 entry_SYSCALL_64_after_hwframe+0x49/0xbe The buggy address belongs to the object at ffff88809b8b9700 which belongs to the cache kmalloc-64 of size 64 The buggy address is located 0 bytes inside of 64-byte region [ffff88809b8b9700, ffff88809b8b9740) The buggy address belongs to the page: page:ffffea00026e2e40 count:1 mapcount:0 mapping:ffff88813bff6340 index:0xffff88809b8b9600 flags: 0xfff00000000100(slab) raw: 00fff00000000100 ffffea000288aec8 ffffea00026ad548 ffff88813bff6340 raw: ffff88809b8b9600 ffff88809b8b9000 000000010000001d 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff88809b8b9600: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ffff88809b8b9680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc >ffff88809b8b9700: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ^ ffff88809b8b9780: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ffff88809b8b9800: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ==================================================================