memory leak in do_eventfd

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    5a9ffb95 Merge tag '5.7-rc5-smb3-fixes' of git://git.samba..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10b72a02100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f8295ae5b3f8268d
dashboard link: https://syzkaller.appspot.com/bug?extid=f196caa45793d6374707
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17585b76100000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12500a02100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+f196caa45793d6374707@xxxxxxxxxxxxxxxxxxxxxxxxx

BUG: memory leak
unreferenced object 0xffff888117169ac0 (size 64):
  comm "syz-executor012", pid 6609, jiffies 4294942172 (age 13.720s)
  hex dump (first 32 bytes):
    01 00 00 00 ff ff ff ff 00 00 00 00 00 c9 ff ff  ................
    d0 9a 16 17 81 88 ff ff d0 9a 16 17 81 88 ff ff  ................
  backtrace:
    [<00000000351bb234>] kmalloc include/linux/slab.h:555 [inline]
    [<00000000351bb234>] do_eventfd+0x35/0xf0 fs/eventfd.c:418
    [<00000000c2f69a77>] __do_sys_eventfd fs/eventfd.c:443 [inline]
    [<00000000c2f69a77>] __se_sys_eventfd fs/eventfd.c:441 [inline]
    [<00000000c2f69a77>] __x64_sys_eventfd+0x14/0x20 fs/eventfd.c:441
    [<0000000086d6f989>] do_syscall_64+0x6e/0x220 arch/x86/entry/common.c:295
    [<000000006c5bcb63>] entry_SYSCALL_64_after_hwframe+0x44/0xa9

BUG: memory leak
unreferenced object 0xffff888117169100 (size 64):
  comm "syz-executor012", pid 6609, jiffies 4294942172 (age 13.720s)
  hex dump (first 32 bytes):
    e8 99 dd 00 00 c9 ff ff e8 99 dd 00 00 c9 ff ff  ................
    00 00 00 20 00 00 00 00 00 00 00 00 00 00 00 00  ... ............
  backtrace:
    [<00000000436d2955>] kmalloc include/linux/slab.h:555 [inline]
    [<00000000436d2955>] kzalloc include/linux/slab.h:669 [inline]
    [<00000000436d2955>] kvm_assign_ioeventfd_idx+0x4f/0x270 arch/x86/kvm/../../../virt/kvm/eventfd.c:798
    [<00000000e89390cc>] kvm_assign_ioeventfd arch/x86/kvm/../../../virt/kvm/eventfd.c:934 [inline]
    [<00000000e89390cc>] kvm_ioeventfd+0xbb/0x194 arch/x86/kvm/../../../virt/kvm/eventfd.c:961
    [<00000000ba9f6732>] kvm_vm_ioctl+0x1e6/0x1030 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3670
    [<000000005da94937>] vfs_ioctl fs/ioctl.c:47 [inline]
    [<000000005da94937>] ksys_ioctl+0xa6/0xd0 fs/ioctl.c:771
    [<00000000a583d097>] __do_sys_ioctl fs/ioctl.c:780 [inline]
    [<00000000a583d097>] __se_sys_ioctl fs/ioctl.c:778 [inline]
    [<00000000a583d097>] __x64_sys_ioctl+0x1a/0x20 fs/ioctl.c:778
    [<0000000086d6f989>] do_syscall_64+0x6e/0x220 arch/x86/entry/common.c:295
    [<000000006c5bcb63>] entry_SYSCALL_64_after_hwframe+0x44/0xa9



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