bisecting fixing commit since f8788d86ab28f61f7b46eb6be375f8a726783636
building syzkaller on 59b57593586656c1d5be820aeed0e751087e6ac6
testing commit f8788d86ab28f61f7b46eb6be375f8a726783636 with gcc (GCC) 8.1.0
kernel signature: 7d7b2b7d3d19e576154d48d2e5628f9106dd2586def26ad2e4fc679b520326a9
all runs: crashed: KASAN: slab-out-of-bounds Write in decode_data
testing current HEAD f5e94d10e4c468357019e5c28d48499f677b284f
testing commit f5e94d10e4c468357019e5c28d48499f677b284f with gcc (GCC) 8.1.0
kernel signature: 7f2a39ff8593e5fa3eec8677f1b31b0fa68dcf2217f838e810dfddf643c9641e
all runs: crashed: KASAN: slab-out-of-bounds Write in decode_data
revisions tested: 2, total time: 19m16.958710845s (build: 12m24.77004209s, test: 6m21.894192078s)
the crash still happens on HEAD
commit msg: Merge tag 'drm-next-2020-04-08' of git://anongit.freedesktop.org/drm/drm
crash: KASAN: slab-out-of-bounds Write in decode_data
==================================================================
BUG: KASAN: slab-out-of-bounds in decode_data.part.1+0x23c/0x280 drivers/net/hamradio/6pack.c:843
Write of size 1 at addr ffff888073c0d4ce by task kworker/u4:4/245

CPU: 1 PID: 245 Comm: kworker/u4:4 Not tainted 5.6.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_unbound flush_to_ldisc
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x12d/0x187 lib/dump_stack.c:118
 print_address_description.constprop.8.cold.10+0x9/0x31d mm/kasan/report.c:382
 __kasan_report.cold.11+0x37/0x4e mm/kasan/report.c:511
 kasan_report+0x38/0x50 mm/kasan/common.c:625
 __asan_report_store1_noabort+0x17/0x20 mm/kasan/generic_report.c:148
 decode_data.part.1+0x23c/0x280 drivers/net/hamradio/6pack.c:843
 decode_data drivers/net/hamradio/6pack.c:965 [inline]
 sixpack_decode drivers/net/hamradio/6pack.c:968 [inline]
 sixpack_receive_buf+0x7a8/0x12c0 drivers/net/hamradio/6pack.c:458
 tty_ldisc_receive_buf+0xff/0x1b0 drivers/tty/tty_buffer.c:465
 tty_port_default_receive_buf+0x5f/0x90 drivers/tty/tty_port.c:38
 receive_buf drivers/tty/tty_buffer.c:481 [inline]
 flush_to_ldisc+0x1aa/0x3a0 drivers/tty/tty_buffer.c:533
 process_one_work+0x893/0x1690 kernel/workqueue.c:2266
 worker_thread+0x85/0xb60 kernel/workqueue.c:2412
 kthread+0x354/0x420 kernel/kthread.c:268
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 8410:
 save_stack+0x21/0x50 mm/kasan/common.c:49
 set_track mm/kasan/common.c:57 [inline]
 __kasan_kmalloc.constprop.17+0xc7/0xd0 mm/kasan/common.c:495
 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:509
 __do_kmalloc_node mm/slab.c:3616 [inline]
 __kmalloc_node+0x4d/0x70 mm/slab.c:3623
 kmalloc_node include/linux/slab.h:578 [inline]
 kvmalloc_node+0x6a/0x80 mm/util.c:574
 kvmalloc include/linux/mm.h:739 [inline]
 kvzalloc include/linux/mm.h:747 [inline]
 alloc_netdev_mqs+0x5d/0xd00 net/core/dev.c:9807
 sixpack_open+0xe0/0xa00 drivers/net/hamradio/6pack.c:563
 tty_ldisc_open.isra.3+0x78/0xc0 drivers/tty/tty_ldisc.c:464
 tty_set_ldisc+0x238/0x5b0 drivers/tty/tty_ldisc.c:591
 tiocsetd drivers/tty/tty_io.c:2333 [inline]
 tty_ioctl+0x332/0x12f0 drivers/tty/tty_io.c:2593
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0xc1/0x110 fs/ioctl.c:763
 __do_sys_ioctl fs/ioctl.c:772 [inline]
 __se_sys_ioctl fs/ioctl.c:770 [inline]
 __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:770
 do_syscall_64+0xca/0x630 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xb3

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff888073c0c000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 1230 bytes to the right of
 4096-byte region [ffff888073c0c000, ffff888073c0d000)
The buggy address belongs to the page:
page:ffffea0001cf0300 refcount:1 mapcount:0 mapping:00000000f1fcc5ee index:0x0 head:ffffea0001cf0300 order:1 compound_mapcount:0
flags: 0xfffe0000010200(slab|head)
raw: 00fffe0000010200 ffffea0001cf0288 ffffea0001cf0408 ffff8880aa402000
raw: 0000000000000000 ffff888073c0c000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888073c0d380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888073c0d400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888073c0d480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                              ^
 ffff888073c0d500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888073c0d580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================