kernel panic: stack is corrupted in pointer

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger  
crash:

Reported-and-tested-by:  
syzbot+79f5f028005a77ecb6bb at syzkaller.appspotmail.com

Tested on:

commit:         decb705e libbpf: fix using uninitialized ioctl results
git tree:       bpf
kernel config:  https://syzkaller.appspot.com/x/.config?x=87305c3ca9c25c70
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

Note: testing is done by a robot and is best-effort only.