[syzbot] memory leak in __send_signal

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    9d32fa5d Merge tag 'net-5.13-rc5' of git://git.kernel.org/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10fd97dfd00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=de8efb0998945e75
dashboard link: https://syzkaller.appspot.com/bug?extid=0bac5fec63d4f399ba98
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16029ce0300000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0bac5fec63d4f399ba98@xxxxxxxxxxxxxxxxxxxxxxxxx

2021/06/05 21:42:36 executed programs: 303
2021/06/05 21:42:42 executed programs: 312
2021/06/05 21:42:48 executed programs: 319
2021/06/05 21:42:54 executed programs: 331
BUG: memory leak
unreferenced object 0xffff8881278e3c80 (size 80):
  comm "syz-executor.4", pid 12851, jiffies 4295068441 (age 14.610s)
  hex dump (first 32 bytes):
    80 3c 8e 27 81 88 ff ff 80 3c 8e 27 81 88 ff ff  .<.'.....<.'....
    00 00 00 00 00 00 00 00 05 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffff812450d6>] __sigqueue_alloc+0xd6/0x240 kernel/signal.c:441
    [<ffffffff81247d31>] __send_signal+0x231/0x600 kernel/signal.c:1155
    [<ffffffff8124b123>] do_send_sig_info+0x63/0xc0 kernel/signal.c:1333
    [<ffffffff8124b4f9>] do_send_specific+0xc9/0xf0 kernel/signal.c:3881
    [<ffffffff8124b5ab>] do_tkill+0x8b/0xb0 kernel/signal.c:3907
    [<ffffffff8124e811>] __do_sys_tkill kernel/signal.c:3942 [inline]
    [<ffffffff8124e811>] __se_sys_tkill kernel/signal.c:3936 [inline]
    [<ffffffff8124e811>] __x64_sys_tkill+0x31/0x50 kernel/signal.c:3936
    [<ffffffff843540da>] do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47
    [<ffffffff84400068>] entry_SYSCALL_64_after_hwframe+0x44/0xae



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