bisecting fixing commit since 0cc244011f40280b78fc344d5c2aac5a0c659f77 building syzkaller on 6a81331a1d4c744da9204d02ec88d558f7eea9c9 testing commit 0cc244011f40280b78fc344d5c2aac5a0c659f77 with gcc (GCC) 8.4.1 20210217 kernel signature: 128a2eab5a5b5bad596188b765fa0aa075f3ac46a8e0ec3cf5e656f8bf9eed2c run #0: crashed: KASAN: use-after-free Write in ex_handler_refcount run #1: crashed: KASAN: use-after-free Read in nbd_put run #2: crashed: KASAN: use-after-free Write in ex_handler_refcount run #3: crashed: KASAN: use-after-free Read in nbd_put run #4: crashed: KASAN: use-after-free Read in nbd_put run #5: crashed: KASAN: use-after-free Write in ex_handler_refcount run #6: crashed: KASAN: use-after-free Read in nbd_put run #7: crashed: WARNING: refcount bug in nbd_put run #8: crashed: KASAN: use-after-free Write in ex_handler_refcount run #9: crashed: KASAN: use-after-free Write in ex_handler_refcount run #10: crashed: KASAN: use-after-free Read in nbd_put run #11: crashed: KASAN: use-after-free Write in ex_handler_refcount run #12: crashed: KASAN: use-after-free Read in nbd_put run #13: crashed: WARNING: refcount bug in nbd_put run #14: crashed: KASAN: use-after-free Read in nbd_put run #15: crashed: KASAN: use-after-free Read in nbd_put run #16: crashed: KASAN: use-after-free Read in nbd_put run #17: crashed: KASAN: use-after-free Read in nbd_put run #18: crashed: KASAN: use-after-free Write in ex_handler_refcount run #19: crashed: KASAN: use-after-free Read in nbd_put testing current HEAD 7d7d1c0ab3eb7c8d8f63a126535018007823b207 testing commit 7d7d1c0ab3eb7c8d8f63a126535018007823b207 with gcc (GCC) 8.4.1 20210217 kernel signature: b95b4e9cc6a8eb13a263c5443b06e649004c99f9f8ce4a355776b592ab8bf577 run #0: crashed: KASAN: use-after-free Read in nbd_put run #1: crashed: KASAN: use-after-free Read in nbd_put run #2: crashed: WARNING: refcount bug in nbd_put run #3: crashed: WARNING: refcount bug in nbd_put run #4: crashed: KASAN: use-after-free Read in nbd_put run #5: crashed: KASAN: use-after-free Write in ex_handler_refcount run #6: crashed: KASAN: use-after-free Write in ex_handler_refcount run #7: crashed: KASAN: use-after-free Write in ex_handler_refcount run #8: crashed: KASAN: use-after-free Write in ex_handler_refcount run #9: crashed: KASAN: use-after-free Read in nbd_put revisions tested: 2, total time: 25m6.29313066s (build: 18m2.647531039s, test: 6m34.755001098s) the crash still happens on HEAD commit msg: Linux 4.14.232 crash: KASAN: use-after-free Read in nbd_put IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_batadv: link becomes ready Bluetooth: hci0 command 0x0409 tx timeout Bluetooth: hci0 command 0x041b tx timeout ================================================================== Bluetooth: hci0 command 0x040f tx timeout BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:183 [inline] BUG: KASAN: use-after-free in atomic_read arch/x86/include/asm/atomic.h:27 [inline] BUG: KASAN: use-after-free in refcount_dec_not_one+0x67/0x70 lib/refcount.c:270 Read of size 4 at addr ffff8880afcc9dd8 by task syz-executor.1/11450 CPU: 0 PID: 11450 Comm: syz-executor.1 Not tainted 4.14.232-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0x14b/0x1e7 lib/dump_stack.c:58 print_address_description.cold.6+0x9/0x1ca mm/kasan/report.c:252 kasan_report_error mm/kasan/report.c:351 [inline] kasan_report mm/kasan/report.c:409 [inline] kasan_report.cold.7+0x11a/0x2d3 mm/kasan/report.c:393 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:429 __read_once_size include/linux/compiler.h:183 [inline] atomic_read arch/x86/include/asm/atomic.h:27 [inline] refcount_dec_not_one+0x67/0x70 lib/refcount.c:270 refcount_dec_and_mutex_lock+0x17/0x50 lib/refcount.c:309 nbd_put+0x1f/0x150 drivers/block/nbd.c:228 nbd_genl_connect+0xcde/0x1540 drivers/block/nbd.c:1896 genl_family_rcv_msg+0x57f/0xfe0 net/netlink/genetlink.c:600 genl_rcv_msg+0xa7/0x140 net/netlink/genetlink.c:625 netlink_rcv_skb+0x12f/0x3b0 net/netlink/af_netlink.c:2433 genl_rcv+0x23/0x40 net/netlink/genetlink.c:636 netlink_unicast_kernel net/netlink/af_netlink.c:1287 [inline] netlink_unicast+0x40b/0x610 net/netlink/af_netlink.c:1313 netlink_sendmsg+0x639/0xbe0 net/netlink/af_netlink.c:1878 sock_sendmsg_nosec net/socket.c:646 [inline] sock_sendmsg+0xac/0xf0 net/socket.c:656 ___sys_sendmsg+0x625/0x920 net/socket.c:2062 __sys_sendmsg+0xc1/0x140 net/socket.c:2096 SYSC_sendmsg net/socket.c:2107 [inline] SyS_sendmsg+0xd/0x20 net/socket.c:2103 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x46/0xbb RIP: 0033:0x466459 RSP: 002b:00007ff7b3da9188 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 000000000056bf60 RCX: 0000000000466459 RDX: 0000000000000000 RSI: 0000000020000100 RDI: 0000000000000005 RBP: 00000000004bf9fb R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf60 R13: 00007fffa93bed9f R14: 00007ff7b3da9300 R15: 0000000000022000 Allocated by task 11447: save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 save_stack mm/kasan/kasan.c:447 [inline] set_track mm/kasan/kasan.c:459 [inline] kasan_kmalloc.part.1+0x62/0xf0 mm/kasan/kasan.c:551 kasan_kmalloc+0xaf/0xc0 mm/kasan/kasan.c:536 kmem_cache_alloc_trace+0x152/0x3f0 mm/slab.c:3618 kmalloc include/linux/slab.h:488 [inline] kzalloc include/linux/slab.h:661 [inline] nbd_dev_add+0x8a/0x7c0 drivers/block/nbd.c:1611 nbd_genl_connect+0x394/0x1540 drivers/block/nbd.c:1756 genl_family_rcv_msg+0x57f/0xfe0 net/netlink/genetlink.c:600 genl_rcv_msg+0xa7/0x140 net/netlink/genetlink.c:625 netlink_rcv_skb+0x12f/0x3b0 net/netlink/af_netlink.c:2433 genl_rcv+0x23/0x40 net/netlink/genetlink.c:636 netlink_unicast_kernel net/netlink/af_netlink.c:1287 [inline] netlink_unicast+0x40b/0x610 net/netlink/af_netlink.c:1313 netlink_sendmsg+0x639/0xbe0 net/netlink/af_netlink.c:1878 sock_sendmsg_nosec net/socket.c:646 [inline] sock_sendmsg+0xac/0xf0 net/socket.c:656 ___sys_sendmsg+0x625/0x920 net/socket.c:2062 __sys_sendmsg+0xc1/0x140 net/socket.c:2096 SYSC_sendmsg net/socket.c:2107 [inline] SyS_sendmsg+0xd/0x20 net/socket.c:2103 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x46/0xbb Freed by task 11450: save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 save_stack mm/kasan/kasan.c:447 [inline] set_track mm/kasan/kasan.c:459 [inline] kasan_slab_free+0xab/0x190 mm/kasan/kasan.c:524 __cache_free mm/slab.c:3496 [inline] kfree+0xcc/0x270 mm/slab.c:3815 nbd_dev_remove drivers/block/nbd.c:223 [inline] nbd_put drivers/block/nbd.c:231 [inline] nbd_put+0x113/0x150 drivers/block/nbd.c:226 nbd_config_put+0x4bf/0x780 drivers/block/nbd.c:1172 nbd_genl_connect+0xcbe/0x1540 drivers/block/nbd.c:1894 genl_family_rcv_msg+0x57f/0xfe0 net/netlink/genetlink.c:600 genl_rcv_msg+0xa7/0x140 net/netlink/genetlink.c:625 netlink_rcv_skb+0x12f/0x3b0 net/netlink/af_netlink.c:2433 genl_rcv+0x23/0x40 net/netlink/genetlink.c:636 netlink_unicast_kernel net/netlink/af_netlink.c:1287 [inline] netlink_unicast+0x40b/0x610 net/netlink/af_netlink.c:1313 netlink_sendmsg+0x639/0xbe0 net/netlink/af_netlink.c:1878 sock_sendmsg_nosec net/socket.c:646 [inline] sock_sendmsg+0xac/0xf0 net/socket.c:656 ___sys_sendmsg+0x625/0x920 net/socket.c:2062 __sys_sendmsg+0xc1/0x140 net/socket.c:2096 SYSC_sendmsg net/socket.c:2107 [inline] SyS_sendmsg+0xd/0x20 net/socket.c:2103 do_syscall_64+0x1c7/0x5b0 arch/x86/entry/common.c:292 entry_SYSCALL_64_after_hwframe+0x46/0xbb The buggy address belongs to the object at ffff8880afcc9d00 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 216 bytes inside of 512-byte region [ffff8880afcc9d00, ffff8880afcc9f00) The buggy address belongs to the page: page:ffffea0002bf3240 count:1 mapcount:0 mapping:ffff8880afcc9080 index:0x0 flags: 0xfff00000000100(slab) raw: 00fff00000000100 ffff8880afcc9080 0000000000000000 0000000100000006 raw: ffffea0002bf29e0 ffffea0002bf32e0 ffff88813fe60940 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff8880afcc9c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff8880afcc9d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff8880afcc9d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8880afcc9e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8880afcc9e80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================