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BUG: KASAN: use-after-free in tcp_skb_pcount include/net/tcp.h:912 [inline]
BUG: KASAN: use-after-free in tcp_init_tso_segs+0x19d/0x1f0 net/ipv4/tcp_output.c:1790
Read of size 2 at addr ffff8881c72a7430 by task syz-executor.0/4189

CPU: 0 PID: 4189 Comm: syz-executor.0 Not tainted 4.14.144+ #0
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0xca/0x134 lib/dump_stack.c:53
 print_address_description+0x60/0x226 mm/kasan/report.c:187
 __kasan_report.cold+0x1a/0x41 mm/kasan/report.c:316
 tcp_skb_pcount include/net/tcp.h:912 [inline]
 tcp_init_tso_segs+0x19d/0x1f0 net/ipv4/tcp_output.c:1790
 tcp_write_xmit+0x15a/0x4730 net/ipv4/tcp_output.c:2330
 __tcp_push_pending_frames+0xa0/0x230 net/ipv4/tcp_output.c:2563
 tcp_send_fin+0x154/0xbc0 net/ipv4/tcp_output.c:3115
 tcp_shutdown net/ipv4/tcp.c:2117 [inline]
 tcp_shutdown+0xd5/0x100 net/ipv4/tcp.c:2102
 inet_shutdown+0x16f/0x350 net/ipv4/af_inet.c:830
 SYSC_shutdown net/socket.c:1917 [inline]
 SyS_shutdown+0xe6/0x190 net/socket.c:1908
 do_syscall_64+0x19b/0x520 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4598e9
RSP: 002b:00007f78a7aabc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000030
RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00000000004598e9
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000005
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f78a7aac6d4
R13: 00000000004c8463 R14: 00000000004df000 R15: 00000000ffffffff

Allocated by task 4189:
 save_stack mm/kasan/common.c:76 [inline]
 set_track mm/kasan/common.c:85 [inline]
 __kasan_kmalloc.part.0+0x53/0xc0 mm/kasan/common.c:495
 slab_post_alloc_hook mm/slab.h:439 [inline]
 slab_alloc_node mm/slub.c:2792 [inline]
 slab_alloc mm/slub.c:2800 [inline]
 kmem_cache_alloc+0xee/0x360 mm/slub.c:2805
 kmem_cache_alloc_node include/linux/slab.h:361 [inline]
 __alloc_skb+0xea/0x5c0 net/core/skbuff.c:193
 alloc_skb_fclone include/linux/skbuff.h:1022 [inline]
 sk_stream_alloc_skb+0xf4/0x8a0 net/ipv4/tcp.c:855
 tcp_sendmsg_locked+0xf11/0x2f50 net/ipv4/tcp.c:1301
 tcp_sendmsg+0x2b/0x40 net/ipv4/tcp.c:1457
 inet_sendmsg+0x15b/0x520 net/ipv4/af_inet.c:760
 sock_sendmsg_nosec net/socket.c:646 [inline]
 sock_sendmsg+0xb7/0x100 net/socket.c:656
 SYSC_sendto net/socket.c:1763 [inline]
 SyS_sendto+0x1de/0x2f0 net/socket.c:1731
 do_syscall_64+0x19b/0x520 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
 0xffffffffffffffff

Freed by task 4189:
 save_stack mm/kasan/common.c:76 [inline]
 set_track mm/kasan/common.c:85 [inline]
 __kasan_slab_free+0x164/0x210 mm/kasan/common.c:457
 slab_free_hook mm/slub.c:1407 [inline]
 slab_free_freelist_hook mm/slub.c:1458 [inline]
 slab_free mm/slub.c:3039 [inline]
 kmem_cache_free+0xd7/0x3b0 mm/slub.c:3055
 kfree_skbmem+0x84/0x110 net/core/skbuff.c:607
 sk_wmem_free_skb include/net/sock.h:1416 [inline]
 tcp_remove_empty_skb net/ipv4/tcp.c:929 [inline]
 tcp_remove_empty_skb+0x264/0x320 net/ipv4/tcp.c:923
 tcp_sendmsg_locked+0x1c09/0x2f50 net/ipv4/tcp.c:1435
 tcp_sendmsg+0x2b/0x40 net/ipv4/tcp.c:1457
 inet_sendmsg+0x15b/0x520 net/ipv4/af_inet.c:760
 sock_sendmsg_nosec net/socket.c:646 [inline]
 sock_sendmsg+0xb7/0x100 net/socket.c:656
 SYSC_sendto net/socket.c:1763 [inline]
 SyS_sendto+0x1de/0x2f0 net/socket.c:1731
 do_syscall_64+0x19b/0x520 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
 0xffffffffffffffff

The buggy address belongs to the object at ffff8881c72a7400
 which belongs to the cache skbuff_fclone_cache of size 456
The buggy address is located 48 bytes inside of
 456-byte region [ffff8881c72a7400, ffff8881c72a75c8)
The buggy address belongs to the page:
page:ffffea00071ca980 count:1 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 0000000000000000 0000000000000000 00000001800c000c
raw: ffffea0007641380 0000000b0000000b ffff8881dab70400 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881c72a7300: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
 ffff8881c72a7380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8881c72a7400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                     ^
 ffff8881c72a7480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881c72a7500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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