bisecting fixing commit since 4fccc2503536a564a4ba31a1d50439854201659f
building syzkaller on 2c36e7a75f8689b3da20e1a81a2ee5391f3af6e5
testing commit 4fccc2503536a564a4ba31a1d50439854201659f with gcc (GCC) 8.1.0
kernel signature: 825a2079f82eaa39ece54b5031f35000ae8288e4264a814deb0b6239d54eb45c
all runs: crashed: KASAN: slab-out-of-bounds Write in decode_data
testing current HEAD d18b78abc0c6e7d3119367c931c583e02d466495
testing commit d18b78abc0c6e7d3119367c931c583e02d466495 with gcc (GCC) 8.1.0
kernel signature: 6427aa9d0adff68058c4f0e8eecb3eae27d36849063811b8dfbf9b5829f4b16b
all runs: crashed: KASAN: slab-out-of-bounds Write in decode_data
revisions tested: 2, total time: 27m43.931380552s (build: 19m33.611652468s, test: 6m37.77624675s)
the crash still happens on HEAD
commit msg: Linux 4.19.141
crash: KASAN: slab-out-of-bounds Write in decode_data
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
sp0: Synchronizing with TNC
==================================================================
BUG: KASAN: slab-out-of-bounds in decode_data.part.2+0x23c/0x280 drivers/net/hamradio/6pack.c:863
Write of size 1 at addr ffff88808d0a7b0e by task kworker/u4:5/596

CPU: 0 PID: 596 Comm: kworker/u4:5 Not tainted 4.19.141-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+0x123/0x177 lib/dump_stack.c:118
 print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
sp1: Synchronizing with TNC
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
 __asan_report_store1_noabort+0x17/0x20 mm/kasan/report.c:435
 decode_data.part.2+0x23c/0x280 drivers/net/hamradio/6pack.c:863
 decode_data drivers/net/hamradio/6pack.c:985 [inline]
 sixpack_decode drivers/net/hamradio/6pack.c:988 [inline]
 sixpack_receive_buf+0x722/0x1120 drivers/net/hamradio/6pack.c:458
 tty_ldisc_receive_buf+0xff/0x1b0 drivers/tty/tty_buffer.c:460
 tty_port_default_receive_buf+0x5f/0x90 drivers/tty/tty_port.c:38
 receive_buf drivers/tty/tty_buffer.c:476 [inline]
 flush_to_ldisc+0x1aa/0x3a0 drivers/tty/tty_buffer.c:528
 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 7844:
 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
 __do_kmalloc_node mm/slab.c:3689 [inline]
 __kmalloc_node+0x50/0x70 mm/slab.c:3696
 kmalloc_node include/linux/slab.h:557 [inline]
 kvmalloc_node+0x68/0x70 mm/util.c:423
 kvmalloc include/linux/mm.h:577 [inline]
 kvzalloc include/linux/mm.h:585 [inline]
 alloc_netdev_mqs+0x5d/0xc80 net/core/dev.c:9138
 sixpack_open+0xe7/0xbc2 drivers/net/hamradio/6pack.c:563
 tty_ldisc_open.isra.3+0x65/0xa0 drivers/tty/tty_ldisc.c:469
 tty_set_ldisc+0x249/0x5a0 drivers/tty/tty_ldisc.c:594
 tiocsetd drivers/tty/tty_io.c:2359 [inline]
 tty_ioctl+0x31e/0x1290 drivers/tty/tty_io.c:2603
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0x196/0x10c0 fs/ioctl.c:688
 ksys_ioctl+0x62/0x90 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:712 [inline]
 __se_sys_ioctl fs/ioctl.c:710 [inline]
 __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:710
 do_syscall_64+0xd0/0x4e0 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff88808d0a6780
 which belongs to the cache kmalloc-4096 of size 4096
The buggy address is located 910 bytes to the right of
 4096-byte region [ffff88808d0a6780, ffff88808d0a7780)
The buggy address belongs to the page:
page:ffffea0002342980 count:1 mapcount:0 mapping:ffff88812c29cdc0 index:0x0 compound_mapcount: 0
flags: 0xfffe0000008100(slab|head)
raw: 00fffe0000008100 ffffea0002342908 ffffea00022e7e08 ffff88812c29cdc0
raw: 0000000000000000 ffff88808d0a6780 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88808d0a7a00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88808d0a7a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88808d0a7b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                      ^
 ffff88808d0a7b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88808d0a7c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================