bisecting fixing commit since 6dd0e32665e591e9debe3edaf73c2f8135bf047e building syzkaller on 3f3c557402456696073f79aafa65b4d7fa2b8794 testing commit 6dd0e32665e591e9debe3edaf73c2f8135bf047e with gcc (GCC) 8.1.0 kernel signature: d678f7636045c4f281081eb636e792b6616ea5ec0c7ec62673a2c9d4b72543c4 run #0: crashed: KASAN: use-after-free Write in ex_handler_refcount run #1: crashed: KASAN: use-after-free Read in l2cap_chan_close run #2: crashed: KASAN: use-after-free Read in l2cap_chan_close run #3: crashed: KASAN: use-after-free Write in ex_handler_refcount run #4: crashed: KASAN: use-after-free Read in l2cap_chan_close run #5: crashed: KASAN: use-after-free Read in l2cap_chan_close run #6: crashed: KASAN: use-after-free Write in ex_handler_refcount run #7: crashed: KASAN: use-after-free Read in l2cap_chan_close run #8: crashed: KASAN: use-after-free Write in ex_handler_refcount run #9: OK testing current HEAD 17a87580a8856170d59aab302226811a4ae69149 testing commit 17a87580a8856170d59aab302226811a4ae69149 with gcc (GCC) 8.1.0 kernel signature: 130e0652b9b553ce4f7931c5750fe90897402526c1bb8a92f38036651b5455cf run #0: crashed: KASAN: use-after-free Read in l2cap_chan_close run #1: crashed: KASAN: use-after-free Read in l2cap_chan_close run #2: crashed: KASAN: use-after-free Read in l2cap_chan_close run #3: crashed: KASAN: use-after-free Read in l2cap_chan_close run #4: crashed: KASAN: use-after-free Write in ex_handler_refcount run #5: crashed: KASAN: use-after-free Read in l2cap_chan_close run #6: crashed: KASAN: use-after-free Read in l2cap_chan_close run #7: OK run #8: OK run #9: OK revisions tested: 2, total time: 44m35.379792452s (build: 19m54.047693767s, test: 23m17.531486101s) the crash still happens on HEAD commit msg: Linux 4.19.133 crash: KASAN: use-after-free Read in l2cap_chan_close IPv6: ADDRCONF(NETDEV_CHANGE): veth0_to_batadv: link becomes ready IPv6: ADDRCONF(NETDEV_CHANGE): batadv_slave_1: link becomes ready IPv6: ADDRCONF(NETDEV_CHANGE): veth1_to_batadv: link becomes ready ================================================================== BUG: KASAN: use-after-free in l2cap_chan_close+0x536/0x830 net/bluetooth/l2cap_core.c:727 Read of size 1 at addr ffff8880a919e5a0 by task kworker/1:4/7772 CPU: 1 PID: 7772 Comm: kworker/1:4 Not tainted 4.19.133-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Workqueue: events do_enable_set Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x123/0x177 lib/dump_stack.c:118 print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256 kasan_report_error mm/kasan/report.c:354 [inline] kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412 __asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430 l2cap_chan_close+0x536/0x830 net/bluetooth/l2cap_core.c:727 do_enable_set+0x47e/0x8b0 net/bluetooth/6lowpan.c:1086 process_one_work+0x830/0x1670 kernel/workqueue.c:2155 worker_thread+0x85/0xb60 kernel/workqueue.c:2298 kthread+0x324/0x3e0 kernel/kthread.c:246 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415 Allocated by task 14: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553 kmem_cache_alloc_trace+0x152/0x740 mm/slab.c:3625 kmalloc include/linux/slab.h:515 [inline] kzalloc include/linux/slab.h:709 [inline] l2cap_chan_create+0x41/0x340 net/bluetooth/l2cap_core.c:441 chan_create+0xa/0xc0 net/bluetooth/6lowpan.c:652 bt_6lowpan_listen net/bluetooth/6lowpan.c:971 [inline] do_enable_set+0x4af/0x8b0 net/bluetooth/6lowpan.c:1090 process_one_work+0x830/0x1670 kernel/workqueue.c:2155 worker_thread+0x85/0xb60 kernel/workqueue.c:2298 kthread+0x324/0x3e0 kernel/kthread.c:246 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415 Freed by task 14: save_stack+0x43/0xd0 mm/kasan/kasan.c:448 set_track mm/kasan/kasan.c:460 [inline] __kasan_slab_free+0x102/0x150 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 l2cap_chan_destroy+0x132/0x1a0 net/bluetooth/l2cap_core.c:479 kref_put include/linux/kref.h:70 [inline] l2cap_chan_put+0x1e/0x20 net/bluetooth/l2cap_core.c:493 do_enable_set+0x48a/0x8b0 net/bluetooth/6lowpan.c:1087 process_one_work+0x830/0x1670 kernel/workqueue.c:2155 worker_thread+0x85/0xb60 kernel/workqueue.c:2298 kthread+0x324/0x3e0 kernel/kthread.c:246 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415 The buggy address belongs to the object at ffff8880a919e580 which belongs to the cache kmalloc-2048 of size 2048 The buggy address is located 32 bytes inside of 2048-byte region [ffff8880a919e580, ffff8880a919ed80) The buggy address belongs to the page: page:ffffea0002a46780 count:1 mapcount:0 mapping:ffff88812c29cc40 index:0x0 compound_mapcount: 0 flags: 0xfffe0000008100(slab|head) raw: 00fffe0000008100 ffffea0002a2e008 ffffea0002a3dd88 ffff88812c29cc40 raw: 0000000000000000 ffff8880a919e580 0000000100000003 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff8880a919e480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff8880a919e500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff8880a919e580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8880a919e600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8880a919e680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================