[syzbot] memory leak in keyctl_watch_key

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    56e337f2cf13 Revert "gpio: Revert regression in sysfs-gpio..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16b65f8d700000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6c80259f3b3fdf91
dashboard link: https://syzkaller.appspot.com/bug?extid=6e2de48f06cdb2884bfc
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1786c3b5700000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=171ca6b1700000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6e2de48f06cdb2884bfc at syzkaller.appspotmail.com

Warning: Permanently added '10.128.10.13' (ECDSA) to the list of known hosts.
executing program
executing program
BUG: memory leak
unreferenced object 0xffff88810ce4a200 (size 96):
  comm "syz-executor352", pid 3605, jiffies 4294947473 (age 13.720s)
  hex dump (first 32 bytes):
    e0 82 48 0d 81 88 ff ff 00 00 00 00 00 00 00 00  ..H.............
    80 a2 e4 0c 81 88 ff ff 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffff8214e6cc>] kmalloc include/linux/slab.h:581 [inline]
    [<ffffffff8214e6cc>] kzalloc include/linux/slab.h:714 [inline]
    [<ffffffff8214e6cc>] keyctl_watch_key+0xec/0x2e0 security/keys/keyctl.c:1800
    [<ffffffff8214ec84>] __do_sys_keyctl+0x3c4/0x490 security/keys/keyctl.c:2016
    [<ffffffff84493a25>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
    [<ffffffff84493a25>] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
    [<ffffffff84600068>] entry_SYSCALL_64_after_hwframe+0x44/0xae



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