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SubjectRe: KASAN: use-after-free Read in x25_device_event
From
syzbot has found a reproducer for the following crash on:

HEAD commit: d9862cfb Merge tag 'mips_5.1' of git://git.kernel.org/pub/..
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1531cf23200000
kernel config: https://syzkaller.appspot.com/x/.config?x=73d88a42238825ad
dashboard link: https://syzkaller.appspot.com/bug?extid=04babcefcd396fabec37
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: amd64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=100ffdad200000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16c2599d200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+04babcefcd396fabec37@syzkaller.appspotmail.com

device ifb0 entered promiscuous mode
device ifb0 left promiscuous mode
device ifb0 entered promiscuous mode
device ifb0 left promiscuous mode
==================================================================
BUG: KASAN: use-after-free in x25_kill_by_device net/x25/af_x25.c:217
[inline]
BUG: KASAN: use-after-free in x25_device_event+0x296/0x2b0
net/x25/af_x25.c:252
Read of size 8 at addr ffff8880a030edd0 by task syz-executor003/7854

CPU: 0 PID: 7854 Comm: syz-executor003 Not tainted 5.0.0+ #97
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+0x172/0x1f0 lib/dump_stack.c:113
print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187
kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
__asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
x25_kill_by_device net/x25/af_x25.c:217 [inline]
x25_device_event+0x296/0x2b0 net/x25/af_x25.c:252
notifier_call_chain+0xc7/0x240 kernel/notifier.c:93
__raw_notifier_call_chain kernel/notifier.c:394 [inline]
raw_notifier_call_chain+0x2e/0x40 kernel/notifier.c:401
call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1739
call_netdevice_notifiers_extack net/core/dev.c:1751 [inline]
call_netdevice_notifiers net/core/dev.c:1765 [inline]
__dev_notify_flags+0x1e9/0x2c0 net/core/dev.c:7607
dev_change_flags+0x10d/0x170 net/core/dev.c:7643
dev_ifsioc+0x2b0/0x940 net/core/dev_ioctl.c:237
dev_ioctl+0x1b8/0xc70 net/core/dev_ioctl.c:488
sock_do_ioctl+0x1bd/0x300 net/socket.c:995
sock_ioctl+0x32b/0x610 net/socket.c:1096
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0xd6e/0x1390 fs/ioctl.c:696
ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4467c9
Code: e8 0c e8 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 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 0f 83 5b 07 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fdbea222d98 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dbc58 RCX: 00000000004467c9
RDX: 0000000020000340 RSI: 0000000000008914 RDI: 0000000000000003
RBP: 00000000006dbc50 R08: 00007fdbea223700 R09: 0000000000000000
R10: 00007fdbea223700 R11: 0000000000000246 R12: 00000000006dbc5c
R13: 6000030030626669 R14: 0000000000000000 R15: 0000000030626669

Allocated by task 7843:
save_stack+0x45/0xd0 mm/kasan/common.c:73
set_track mm/kasan/common.c:85 [inline]
__kasan_kmalloc mm/kasan/common.c:495 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:468
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:509
kmem_cache_alloc_trace+0x151/0x760 mm/slab.c:3615
kmalloc include/linux/slab.h:545 [inline]
x25_link_device_up+0x46/0x3f0 net/x25/x25_link.c:249
x25_device_event+0x116/0x2b0 net/x25/af_x25.c:242
notifier_call_chain+0xc7/0x240 kernel/notifier.c:93
__raw_notifier_call_chain kernel/notifier.c:394 [inline]
raw_notifier_call_chain+0x2e/0x40 kernel/notifier.c:401
call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1739
call_netdevice_notifiers_extack net/core/dev.c:1751 [inline]
call_netdevice_notifiers net/core/dev.c:1765 [inline]
__dev_notify_flags+0x121/0x2c0 net/core/dev.c:7605
dev_change_flags+0x10d/0x170 net/core/dev.c:7643
dev_ifsioc+0x2b0/0x940 net/core/dev_ioctl.c:237
dev_ioctl+0x1b8/0xc70 net/core/dev_ioctl.c:488
sock_do_ioctl+0x1bd/0x300 net/socket.c:995
sock_ioctl+0x32b/0x610 net/socket.c:1096
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0xd6e/0x1390 fs/ioctl.c:696
ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 7865:
save_stack+0x45/0xd0 mm/kasan/common.c:73
set_track mm/kasan/common.c:85 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:457
kasan_slab_free+0xe/0x10 mm/kasan/common.c:465
__cache_free mm/slab.c:3494 [inline]
kfree+0xcf/0x230 mm/slab.c:3811
x25_neigh_put include/net/x25.h:253 [inline]
x25_connect+0x8d8/0xde0 net/x25/af_x25.c:824
__sys_connect+0x266/0x330 net/socket.c:1685
__do_sys_connect net/socket.c:1696 [inline]
__se_sys_connect net/socket.c:1693 [inline]
__x64_sys_connect+0x73/0xb0 net/socket.c:1693
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a030edc0
which belongs to the cache kmalloc-256 of size 256
The buggy address is located 16 bytes inside of
256-byte region [ffff8880a030edc0, ffff8880a030eec0)
The buggy address belongs to the page:
page:ffffea000280c380 count:1 mapcount:0 mapping:ffff88812c3f07c0 index:0x0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea0002806788 ffffea00027f0188 ffff88812c3f07c0
raw: 0000000000000000 ffff8880a030e000 000000010000000c 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a030ec80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880a030ed00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8880a030ed80: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
^
ffff8880a030ee00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880a030ee80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================

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