[syzbot] memory leak in mld_newpack

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    8cae8cd89f05 seq_file: disallow extremely large seq buffer..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1100e00a300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7384ed231a0fd986
dashboard link: https://syzkaller.appspot.com/bug?extid=dcd3e13cf4472f2e0ba1
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14c646a2300000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+dcd3e13cf4472f2e0ba1@xxxxxxxxxxxxxxxxxxxxxxxxx

2021/07/22 00:14:37 executed programs: 3
2021/07/22 00:14:42 executed programs: 5
2021/07/22 00:14:48 executed programs: 7
BUG: memory leak
unreferenced object 0xffff88810df2ad00 (size 232):
  comm "kworker/1:2", pid 2838, jiffies 4294938475 (age 902.280s)
  hex dump (first 32 bytes):
    a0 34 1f 19 81 88 ff ff a0 34 1f 19 81 88 ff ff  .4.......4......
    00 40 1c 10 81 88 ff ff 00 00 00 00 00 00 00 00  .@..............
  backtrace:
    [<ffffffff836e0f5f>] __alloc_skb+0x20f/0x280 net/core/skbuff.c:414
    [<ffffffff836eb79a>] alloc_skb include/linux/skbuff.h:1112 [inline]
    [<ffffffff836eb79a>] alloc_skb_with_frags+0x6a/0x2b0 net/core/skbuff.c:6005
    [<ffffffff836d9083>] sock_alloc_send_pskb+0x353/0x3c0 net/core/sock.c:2461
    [<ffffffff83b7fd64>] mld_newpack+0x84/0x200 net/ipv6/mcast.c:1751
    [<ffffffff83b7ff83>] add_grhead+0xa3/0xc0 net/ipv6/mcast.c:1854
    [<ffffffff83b80c26>] add_grec+0x7b6/0x820 net/ipv6/mcast.c:1992
    [<ffffffff83b830d3>] mld_send_cr net/ipv6/mcast.c:2118 [inline]
    [<ffffffff83b830d3>] mld_ifc_work+0x273/0x750 net/ipv6/mcast.c:2655
    [<ffffffff81262669>] process_one_work+0x2c9/0x610 kernel/workqueue.c:2276
    [<ffffffff81262f59>] worker_thread+0x59/0x5d0 kernel/workqueue.c:2422
    [<ffffffff8126c3b8>] kthread+0x188/0x1d0 kernel/kthread.c:319
    [<ffffffff810022cf>] ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

BUG: memory leak
unreferenced object 0xffff88811109ca00 (size 232):
  comm "kworker/1:2", pid 2838, jiffies 4294938656 (age 900.470s)
  hex dump (first 32 bytes):
    a0 ac 9e 16 81 88 ff ff a0 ac 9e 16 81 88 ff ff  ................
    00 00 37 13 81 88 ff ff 00 00 00 00 00 00 00 00  ..7.............
  backtrace:
    [<ffffffff836e0f5f>] __alloc_skb+0x20f/0x280 net/core/skbuff.c:414
    [<ffffffff83b6bb36>] alloc_skb include/linux/skbuff.h:1112 [inline]
    [<ffffffff83b6bb36>] ndisc_alloc_skb+0x56/0xe0 net/ipv6/ndisc.c:420
    [<ffffffff83b7085c>] ndisc_send_rs+0x1bc/0x2a0 net/ipv6/ndisc.c:686
    [<ffffffff83b46bae>] addrconf_dad_completed+0x17e/0x560 net/ipv6/addrconf.c:4195
    [<ffffffff83b4736d>] addrconf_dad_work+0x3dd/0x900 net/ipv6/addrconf.c:4105
    [<ffffffff81262669>] process_one_work+0x2c9/0x610 kernel/workqueue.c:2276
    [<ffffffff81262f59>] worker_thread+0x59/0x5d0 kernel/workqueue.c:2422
    [<ffffffff8126c3b8>] kthread+0x188/0x1d0 kernel/kthread.c:319
    [<ffffffff810022cf>] ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295



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