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BUG: KASAN: use-after-free in sl_sync drivers/net/slip/slip.c:725 [inline]
BUG: KASAN: use-after-free in slip_open+0xe92/0x1175 drivers/net/slip/slip.c:801
Read of size 8 at addr ffff888096db76c8 by task syz-executor.4/32131

CPU: 1 PID: 32131 Comm: syz-executor.4 Not tainted 4.19.85-syzkaller #0
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+0x197/0x210 lib/dump_stack.c:118
 print_address_description.cold+0x7c/0x20d mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report mm/kasan/report.c:412 [inline]
 kasan_report.cold+0x8c/0x2ba mm/kasan/report.c:396
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 sl_sync drivers/net/slip/slip.c:725 [inline]
 slip_open+0xe92/0x1175 drivers/net/slip/slip.c:801
 tty_ldisc_open.isra.0+0x89/0xd0 drivers/tty/tty_ldisc.c:462
 tty_set_ldisc+0x2e3/0x690 drivers/tty/tty_ldisc.c:587
 tiocsetd drivers/tty/tty_io.c:2359 [inline]
 tty_ioctl+0x65e/0x1510 drivers/tty/tty_io.c:2603
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:688
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:712 [inline]
 __se_sys_ioctl fs/ioctl.c:710 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:710
 do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a639
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fdef289dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a639
RDX: 00000000200003c0 RSI: 0000000000005423 RDI: 0000000000000004
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fdef289e6d4
R13: 00000000004c52d0 R14: 00000000004da3f0 R15: 00000000ffffffff

Allocated by task 31447:
 save_stack+0x45/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 kasan_kmalloc mm/kasan/kasan.c:553 [inline]
 kasan_kmalloc+0xce/0xf0 mm/kasan/kasan.c:531
 __do_kmalloc_node mm/slab.c:3689 [inline]
 __kmalloc_node+0x51/0x80 mm/slab.c:3696
 kmalloc_node include/linux/slab.h:557 [inline]
 kvmalloc_node+0x68/0x100 mm/util.c:423
 kvmalloc include/linux/mm.h:577 [inline]
 kvzalloc include/linux/mm.h:585 [inline]
 alloc_netdev_mqs+0x98/0xd40 net/core/dev.c:8945
 sl_alloc drivers/net/slip/slip.c:751 [inline]
 slip_open+0x38e/0x1175 drivers/net/slip/slip.c:812
 tty_ldisc_open.isra.0+0x89/0xd0 drivers/tty/tty_ldisc.c:462
 tty_set_ldisc+0x2e3/0x690 drivers/tty/tty_ldisc.c:587
 tiocsetd drivers/tty/tty_io.c:2359 [inline]
 tty_ioctl+0x65e/0x1510 drivers/tty/tty_io.c:2603
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:688
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:712 [inline]
 __se_sys_ioctl fs/ioctl.c:710 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:710
 do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 31447:
 save_stack+0x45/0xd0 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
 kvfree+0x61/0x70 mm/util.c:452
 netdev_freemem net/core/dev.c:8899 [inline]
 free_netdev+0x384/0x430 net/core/dev.c:9048
 slip_open+0xd2a/0x1175 drivers/net/slip/slip.c:858
 tty_ldisc_open.isra.0+0x89/0xd0 drivers/tty/tty_ldisc.c:462
 tty_set_ldisc+0x2e3/0x690 drivers/tty/tty_ldisc.c:587
 tiocsetd drivers/tty/tty_io.c:2359 [inline]
 tty_ioctl+0x65e/0x1510 drivers/tty/tty_io.c:2603
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:688
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:712 [inline]
 __se_sys_ioctl fs/ioctl.c:710 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:710
 do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff888096db6c00
 which belongs to the cache kmalloc-4096 of size 4096
The buggy address is located 2760 bytes inside of
 4096-byte region [ffff888096db6c00, ffff888096db7c00)
The buggy address belongs to the page:
page:ffffea00025b6d80 count:1 mapcount:0 mapping:ffff88812c3f0dc0 index:0x0 compound_mapcount: 0
flags: 0x1fffc0000008100(slab|head)
raw: 01fffc0000008100 ffffea00027fb508 ffffea000034d508 ffff88812c3f0dc0
raw: 0000000000000000 ffff888096db6c00 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888096db7580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888096db7600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888096db7680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff888096db7700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888096db7780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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