bisecting fixing commit since 0f1b4cb77d7f5a442b03f8ad597768b422e8ec58 building syzkaller on c59079a693ad1d89c782f7db14b9f1c5629e2abc testing commit 0f1b4cb77d7f5a442b03f8ad597768b422e8ec58 compiler: gcc version 8.4.1 20210217 (GCC) kernel signature: 66ac7995b8826be4aa83a7ec8b01f716924930b98c7f796fa7b96053c5cad9ea 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 Read in nbd_put 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 Read in nbd_put 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 Read in nbd_put run #10: crashed: KASAN: use-after-free Write in ex_handler_refcount 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 Write in ex_handler_refcount testing current HEAD b172b44fcb1771e083aad806fa96f3f60e2ddfac testing commit b172b44fcb1771e083aad806fa96f3f60e2ddfac compiler: gcc version 8.4.1 20210217 (GCC) kernel signature: ef39d96cdb81e8349083691a727c25b0156c7c01db13a3531d53cee0fa751b6c 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: KASAN: use-after-free Write in ex_handler_refcount run #3: crashed: KASAN: use-after-free Write in ex_handler_refcount run #4: crashed: KASAN: use-after-free Read in nbd_put run #5: crashed: KASAN: use-after-free Read in nbd_put run #6: crashed: KASAN: use-after-free Read in nbd_put run #7: crashed: KASAN: use-after-free Write in ex_handler_refcount run #8: crashed: KASAN: use-after-free Read in nbd_put run #9: crashed: KASAN: use-after-free Read in nbd_put revisions tested: 2, total time: 24m13.429173931s (build: 16m29.837018268s, test: 7m12.309875758s) the crash still happens on HEAD commit msg: Linux 4.19.206 crash: KASAN: use-after-free Read in nbd_put netlink: 4 bytes leftover after parsing attributes in process `syz-executor.2'. netlink: 4 bytes leftover after parsing attributes in process `syz-executor.2'. netlink: 4 bytes leftover after parsing attributes in process `syz-executor.3'. ================================================================== BUG: KASAN: use-after-free in atomic_read include/asm-generic/atomic-instrumented.h:21 [inline] BUG: KASAN: use-after-free in refcount_dec_not_one+0x72/0x160 lib/refcount.c:269 Read of size 4 at addr ffff888099b2f618 by task syz-executor.3/11068 CPU: 0 PID: 11068 Comm: syz-executor.3 Not tainted 4.19.206-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 check_memory_region_inline mm/kasan/kasan.c:260 [inline] check_memory_region+0x13c/0x1b0 mm/kasan/kasan.c:267 kasan_check_read+0x11/0x20 mm/kasan/kasan.c:272 atomic_read include/asm-generic/atomic-instrumented.h:21 [inline] refcount_dec_not_one+0x72/0x160 lib/refcount.c:269 refcount_dec_and_mutex_lock+0x17/0x50 lib/refcount.c:308 nbd_put+0x1f/0x150 drivers/block/nbd.c:228 nbd_genl_connect+0xcbf/0x1510 drivers/block/nbd.c:1913 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 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:00007ff51fa81188 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 000000000056bf60 RCX: 0000000000466459 RDX: 0000000000000000 RSI: 0000000020000180 RDI: 0000000000000004 RBP: 00000000004bf9fb R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf60 R13: 00007fff3d49ca0f R14: 00007ff51fa81300 R15: 0000000000022000 Allocated by task 11067: 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] nbd_dev_add+0x4c/0x820 drivers/block/nbd.c:1627 nbd_genl_connect+0x3e8/0x1510 drivers/block/nbd.c:1773 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 11068: 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 nbd_dev_remove drivers/block/nbd.c:223 [inline] nbd_put drivers/block/nbd.c:231 [inline] nbd_put+0x111/0x150 drivers/block/nbd.c:226 nbd_config_put+0x539/0x7a0 drivers/block/nbd.c:1185 nbd_genl_connect+0xca3/0x1510 drivers/block/nbd.c:1911 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 The buggy address belongs to the object at ffff888099b2f540 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 216 bytes inside of 512-byte region [ffff888099b2f540, ffff888099b2f740) The buggy address belongs to the page: page:ffffea000266cbc0 count:1 mapcount:0 mapping:ffff88813bff6940 index:0x0 flags: 0xfff00000000100(slab) raw: 00fff00000000100 ffffea0002641388 ffffea000274ce88 ffff88813bff6940 raw: 0000000000000000 ffff888099b2f040 0000000100000006 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff888099b2f500: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb ffff888099b2f580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff888099b2f600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff888099b2f680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff888099b2f700: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ==================================================================