[PATCH v3] bpf: Fix memory leak in copy_process()

[qiang.zhang@windriver.com]

From: Zqiang <qiang.zhang@windriver.com>

The syzbot report a memleak follow:
BUG: memory leak
unreferenced object 0xffff888101b41d00 (size 120):
  comm "kworker/u4:0", pid 8, jiffies 4294944270 (age 12.780s)
  backtrace:
    [<ffffffff8125dc56>] alloc_pid+0x66/0x560
    [<ffffffff81226405>] copy_process+0x1465/0x25e0
    [<ffffffff81227943>] kernel_clone+0xf3/0x670
    [<ffffffff812281a1>] kernel_thread+0x61/0x80
    [<ffffffff81253464>] call_usermodehelper_exec_work
    [<ffffffff81253464>] call_usermodehelper_exec_work+0xc4/0x120
    [<ffffffff812591c9>] process_one_work+0x2c9/0x600
    [<ffffffff81259ab9>] worker_thread+0x59/0x5d0
    [<ffffffff812611c8>] kthread+0x178/0x1b0
    [<ffffffff8100227f>] ret_from_fork+0x1f/0x30

unreferenced object 0xffff888110ef5c00 (size 232):
  comm "kworker/u4:0", pid 8414, jiffies 4294944270 (age 12.780s)
  backtrace:
    [<ffffffff8154a0cf>] kmem_cache_zalloc
    [<ffffffff8154a0cf>] __alloc_file+0x1f/0xf0
    [<ffffffff8154a809>] alloc_empty_file+0x69/0x120
    [<ffffffff8154a8f3>] alloc_file+0x33/0x1b0
    [<ffffffff8154ab22>] alloc_file_pseudo+0xb2/0x140
    [<ffffffff81559218>] create_pipe_files+0x138/0x2e0
    [<ffffffff8126c793>] umd_setup+0x33/0x220
    [<ffffffff81253574>] call_usermodehelper_exec_async+0xb4/0x1b0
    [<ffffffff8100227f>] ret_from_fork+0x1f/0x30

after the UMD process exits, the pipe_to_umh/pipe_from_umh and tgid
need to be release.

Fixes: d71fa5c9763c ("bpf: Add kernel module with user mode driver that populates bpffs.")
Reported-by: syzbot+44908bb56d2bfe56b28e@syzkaller.appspotmail.com
Signed-off-by: Zqiang <qiang.zhang@windriver.com>
---
 v1->v2:
 Judge whether the pointer variable tgid is valid.
 v2->v3:
 Add common umd_cleanup_helper() and exported as
 symbol which the driver here can use.

 include/linux/usermode_driver.h       |  1 +
 kernel/bpf/preload/bpf_preload_kern.c | 15 +++++++++++----
 kernel/usermode_driver.c              | 18 ++++++++++++++----
 3 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/include/linux/usermode_driver.h b/include/linux/usermode_driver.h
index 073a9e0ec07d..ad970416260d 100644
--- a/include/linux/usermode_driver.h
+++ b/include/linux/usermode_driver.h
@@ -14,5 +14,6 @@ struct umd_info {
 int umd_load_blob(struct umd_info *info, const void *data, size_t len);
 int umd_unload_blob(struct umd_info *info);
 int fork_usermode_driver(struct umd_info *info);
+void umd_cleanup_helper(struct umd_info *info);
 
 #endif /* __LINUX_USERMODE_DRIVER_H__ */
diff --git a/kernel/bpf/preload/bpf_preload_kern.c b/kernel/bpf/preload/bpf_preload_kern.c
index 79c5772465f1..356c4ca4f530 100644
--- a/kernel/bpf/preload/bpf_preload_kern.c
+++ b/kernel/bpf/preload/bpf_preload_kern.c
@@ -61,8 +61,10 @@ static int finish(void)
 	if (n != sizeof(magic))
 		return -EPIPE;
 	tgid = umd_ops.info.tgid;
-	wait_event(tgid->wait_pidfd, thread_group_exited(tgid));
-	umd_ops.info.tgid = NULL;
+	if (tgid) {
+		wait_event(tgid->wait_pidfd, thread_group_exited(tgid));
+		umd_cleanup_helper(&umd_ops.info);
+	}
 	return 0;
 }
 
@@ -80,10 +82,15 @@ static int __init load_umd(void)
 
 static void __exit fini_umd(void)
 {
+	struct pid *tgid;
 	bpf_preload_ops = NULL;
 	/* kill UMD in case it's still there due to earlier error */
-	kill_pid(umd_ops.info.tgid, SIGKILL, 1);
-	umd_ops.info.tgid = NULL;
+	tgid = umd_ops.info.tgid;
+	if (tgid) {
+		kill_pid(tgid, SIGKILL, 1);
+		wait_event(tgid->wait_pidfd, thread_group_exited(tgid));
+		umd_cleanup_helper(&umd_ops.info);
+	}
 	umd_unload_blob(&umd_ops.info);
 }
 late_initcall(load_umd);
diff --git a/kernel/usermode_driver.c b/kernel/usermode_driver.c
index 0b35212ffc3d..6372deae27a0 100644
--- a/kernel/usermode_driver.c
+++ b/kernel/usermode_driver.c
@@ -140,13 +140,23 @@ static void umd_cleanup(struct subprocess_info *info)
 
 	/* cleanup if umh_setup() was successful but exec failed */
 	if (info->retval) {
-		fput(umd_info->pipe_to_umh);
-		fput(umd_info->pipe_from_umh);
-		put_pid(umd_info->tgid);
-		umd_info->tgid = NULL;
+		umd_cleanup_helper(umd_info);
 	}
 }
 
+/**
+ * umd_cleanup_helper - release the resources which allocated in umd_setup
+ * @info: information about usermode driver
+ */
+void umd_cleanup_helper(struct umd_info *info)
+{
+	fput(info->pipe_to_umh);
+	fput(info->pipe_from_umh);
+	put_pid(info->tgid);
+	info->tgid = NULL;
+}
+EXPORT_SYMBOL_GPL(umd_cleanup_helper);
+
 /**
  * fork_usermode_driver - fork a usermode driver
  * @info: information about usermode driver (shouldn't be NULL)
-- 
2.17.1