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SubjectKASAN: slab-out-of-bounds Write in decode_data
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Hello,

syzbot found the following crash on:

HEAD commit: 63de3747 Merge tag 'tag-chrome-platform-for-v5.5' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=165a7c82e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=1d189d07c6717979
dashboard link: https://syzkaller.appspot.com/bug?extid=fc8cd9a673d4577fb2e4
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15379c2ee00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=133cf97ee00000

Bisection is inconclusive: the bug happens on the oldest tested release.

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=150e2861e00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=170e2861e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=130e2861e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+fc8cd9a673d4577fb2e4@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in decode_data.part.0+0x23b/0x270
drivers/net/hamradio/6pack.c:843
Write of size 1 at addr ffff8880993bd04e by task kworker/u4:2/25

CPU: 1 PID: 25 Comm: kworker/u4:2 Not tainted 5.4.0-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+0x197/0x210 lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
__kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:638
__asan_report_store1_noabort+0x17/0x20 mm/kasan/generic_report.c:137
decode_data.part.0+0x23b/0x270 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 drivers/net/hamradio/6pack.c:458 [inline]
sixpack_receive_buf+0xde4/0x1420 drivers/net/hamradio/6pack.c:435
tty_ldisc_receive_buf+0x15f/0x1c0 drivers/tty/tty_buffer.c:465
tty_port_default_receive_buf+0x7d/0xb0 drivers/tty/tty_port.c:38
receive_buf drivers/tty/tty_buffer.c:481 [inline]
flush_to_ldisc+0x222/0x390 drivers/tty/tty_buffer.c:533
process_one_work+0x9af/0x1740 kernel/workqueue.c:2264
worker_thread+0x98/0xe40 kernel/workqueue.c:2410
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 8864:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
__kasan_kmalloc mm/kasan/common.c:512 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:485
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:526
__do_kmalloc_node mm/slab.c:3616 [inline]
__kmalloc_node+0x4e/0x70 mm/slab.c:3623
kmalloc_node include/linux/slab.h:579 [inline]
kvmalloc_node+0x68/0x100 mm/util.c:574
kvmalloc include/linux/mm.h:655 [inline]
kvzalloc include/linux/mm.h:663 [inline]
alloc_netdev_mqs+0x98/0xde0 net/core/dev.c:9730
sixpack_open+0x104/0xaaf drivers/net/hamradio/6pack.c:563
tty_ldisc_open.isra.0+0xa3/0x110 drivers/tty/tty_ldisc.c:464
tty_set_ldisc+0x30e/0x6b0 drivers/tty/tty_ldisc.c:591
tiocsetd drivers/tty/tty_io.c:2337 [inline]
tty_ioctl+0xe8d/0x14f0 drivers/tty/tty_io.c:2597
vfs_ioctl fs/ioctl.c:47 [inline]
file_ioctl fs/ioctl.c:545 [inline]
do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
__do_sys_ioctl fs/ioctl.c:756 [inline]
__se_sys_ioctl fs/ioctl.c:754 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 8605:
save_stack+0x23/0x90 mm/kasan/common.c:71
set_track mm/kasan/common.c:79 [inline]
kasan_set_free_info mm/kasan/common.c:334 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:473
kasan_slab_free+0xe/0x10 mm/kasan/common.c:482
__cache_free mm/slab.c:3426 [inline]
kfree+0x10a/0x2c0 mm/slab.c:3757
skb_free_head+0x93/0xb0 net/core/skbuff.c:591
skb_release_data+0x551/0x8d0 net/core/skbuff.c:611
skb_release_all+0x4d/0x60 net/core/skbuff.c:665
__kfree_skb net/core/skbuff.c:679 [inline]
consume_skb net/core/skbuff.c:838 [inline]
consume_skb+0xfb/0x410 net/core/skbuff.c:832
skb_free_datagram+0x1b/0x100 net/core/datagram.c:328
netlink_recvmsg+0x6c6/0xf50 net/netlink/af_netlink.c:1996
sock_recvmsg_nosec net/socket.c:873 [inline]
sock_recvmsg net/socket.c:891 [inline]
sock_recvmsg+0xce/0x110 net/socket.c:887
____sys_recvmsg+0x236/0x550 net/socket.c:2562
___sys_recvmsg+0xff/0x190 net/socket.c:2603
__sys_recvmsg+0x102/0x1d0 net/socket.c:2650
__do_sys_recvmsg net/socket.c:2660 [inline]
__se_sys_recvmsg net/socket.c:2657 [inline]
__x64_sys_recvmsg+0x78/0xb0 net/socket.c:2657
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880993bc000
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 78 bytes to the right of
4096-byte region [ffff8880993bc000, ffff8880993bd000)
The buggy address belongs to the page:
page:ffffea000264ef00 refcount:1 mapcount:0 mapping:ffff8880aa402000
index:0x0 compound_mapcount: 0
raw: 00fffe0000010200 ffffea000262c288 ffffea00029bc908 ffff8880aa402000
raw: 0000000000000000 ffff8880993bc000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880993bcf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880993bcf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8880993bd000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff8880993bd080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880993bd100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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