Re: KASAN: use-after-free Read in kfree_skb (3)

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    d1fdb6d8 Linux 5.2-rc4
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=138bdc01a00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fa9f7e1b6a8bb586
dashboard link: https://syzkaller.appspot.com/bug?extid=dcb1305dd05699c40640
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13c787f2a00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10e32801a00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+dcb1305dd05699c40640@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: use-after-free in atomic_read  
include/asm-generic/atomic-instrumented.h:26 [inline]
BUG: KASAN: use-after-free in refcount_read include/linux/refcount.h:43  
[inline]
BUG: KASAN: use-after-free in skb_unref include/linux/skbuff.h:1016 [inline]
BUG: KASAN: use-after-free in kfree_skb+0x38/0x390 net/core/skbuff.c:690
Read of size 4 at addr ffff88808d7fb2d4 by task kworker/u4:3/189

CPU: 0 PID: 189 Comm: kworker/u4:3 Not tainted 5.2.0-rc4 #25
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+0x172/0x1f0 lib/dump_stack.c:113
 print_address_description.cold+0x7c/0x20d mm/kasan/report.c:188
 __kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
 kasan_report+0x12/0x20 mm/kasan/common.c:614
 check_memory_region_inline mm/kasan/generic.c:185 [inline]
 check_memory_region+0x123/0x190 mm/kasan/generic.c:191
 kasan_check_read+0x11/0x20 mm/kasan/common.c:94
 atomic_read include/asm-generic/atomic-instrumented.h:26 [inline]
 refcount_read include/linux/refcount.h:43 [inline]
 skb_unref include/linux/skbuff.h:1016 [inline]
 kfree_skb+0x38/0x390 net/core/skbuff.c:690
 bcsp_recv+0x2d8/0x13a0 drivers/bluetooth/hci_bcsp.c:608
 hci_uart_tty_receive+0x225/0x530 drivers/bluetooth/hci_ldisc.c:592
 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+0x989/0x1790 kernel/workqueue.c:2269
 worker_thread+0x98/0xe40 kernel/workqueue.c:2415
 kthread+0x354/0x420 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 189:
 save_stack+0x23/0x90 mm/kasan/common.c:71
 set_track mm/kasan/common.c:79 [inline]
 __kasan_kmalloc mm/kasan/common.c:489 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
 kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:497
 slab_post_alloc_hook mm/slab.h:437 [inline]
 slab_alloc_node mm/slab.c:3269 [inline]
 kmem_cache_alloc_node+0x131/0x710 mm/slab.c:3579
 __alloc_skb+0xd5/0x5e0 net/core/skbuff.c:194
 alloc_skb include/linux/skbuff.h:1054 [inline]
 bt_skb_alloc include/net/bluetooth/bluetooth.h:339 [inline]
 bcsp_recv+0x8c1/0x13a0 drivers/bluetooth/hci_bcsp.c:670
 hci_uart_tty_receive+0x225/0x530 drivers/bluetooth/hci_ldisc.c:592
 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+0x989/0x1790 kernel/workqueue.c:2269
 worker_thread+0x98/0xe40 kernel/workqueue.c:2415
 kthread+0x354/0x420 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Freed by task 8808:
 save_stack+0x23/0x90 mm/kasan/common.c:71
 set_track mm/kasan/common.c:79 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
 __cache_free mm/slab.c:3432 [inline]
 kmem_cache_free+0x86/0x260 mm/slab.c:3698
 kfree_skbmem net/core/skbuff.c:620 [inline]
 kfree_skbmem+0xc5/0x150 net/core/skbuff.c:614
 __kfree_skb net/core/skbuff.c:677 [inline]
 kfree_skb net/core/skbuff.c:694 [inline]
 kfree_skb+0xf0/0x390 net/core/skbuff.c:688
 bcsp_recv+0x2d8/0x13a0 drivers/bluetooth/hci_bcsp.c:608
 hci_uart_tty_receive+0x225/0x530 drivers/bluetooth/hci_ldisc.c:592
 tiocsti drivers/tty/tty_io.c:2195 [inline]
 tty_ioctl+0x921/0x14a0 drivers/tty/tty_io.c:2571
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0xd5f/0x1380 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+0xfd/0x680 arch/x86/entry/common.c:301
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88808d7fb200
 which belongs to the cache skbuff_head_cache of size 224
The buggy address is located 212 bytes inside of
 224-byte region [ffff88808d7fb200, ffff88808d7fb2e0)
The buggy address belongs to the page:
page:ffffea000235fec0 refcount:1 mapcount:0 mapping:ffff88821b6f6540  
index:0x0
flags: 0x1fffc0000000200(slab)
raw: 01fffc0000000200 ffffea000256f0c8 ffffea0002a49888 ffff88821b6f6540
raw: 0000000000000000 ffff88808d7fb0c0 000000010000000c 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88808d7fb180: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88808d7fb200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88808d7fb280: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
                                                 ^
 ffff88808d7fb300: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
 ffff88808d7fb380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================