The syzbot reported a memleak as follows:
BUG: memory leak
unreferenced object 0xffff888101b41d00 (size 120):
comm "kworker/u4:0", pid 8, jiffies 4294944270 (age 12.780s)
backtrace:
[] alloc_pid+0x66/0x560
[] copy_process+0x1465/0x25e0
[] kernel_clone+0xf3/0x670
[] kernel_thread+0x61/0x80
[] call_usermodehelper_exec_work
[] call_usermodehelper_exec_work+0xc4/0x120
[] process_one_work+0x2c9/0x600
[] worker_thread+0x59/0x5d0
[] kthread+0x178/0x1b0
[] ret_from_fork+0x1f/0x30
unreferenced object 0xffff888110ef5c00 (size 232):
comm "kworker/u4:0", pid 8414, jiffies 4294944270 (age 12.780s)
backtrace:
[] kmem_cache_zalloc
[] __alloc_file+0x1f/0xf0
[] alloc_empty_file+0x69/0x120
[] alloc_file+0x33/0x1b0
[] alloc_file_pseudo+0xb2/0x140
[] create_pipe_files+0x138/0x2e0
[] umd_setup+0x33/0x220
[] call_usermodehelper_exec_async+0xb4/0x1b0
[] ret_from_fork+0x1f/0x30
After the UMD process exits, the pipe_to_umh/pipe_from_umh and
tgid need to be released.
Fixes: d71fa5c9763c ("bpf: Add kernel module with user mode driver that populates bpffs.")
Reported-by: syzbot+44908bb56d2bfe56b28e@syzkaller.appspotmail.com
Signed-off-by: Zqiang
Signed-off-by: Daniel Borkmann
Link: https://lore.kernel.org/bpf/20210317030915.2865-1-qiang.zhang@windriver.com