bpf: Fix umd memory leak in copy_process()

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:
    [<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 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 <qiang.zhang@windriver.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210317030915.2865-1-qiang.zhang@windriver.com

diff --git a/include/linux/usermode_driver.h b/include/linux/usermode_driver.h
index 073a9e0ec07d06c6fc8f3a323483bbd3401e0df5..ad970416260dd208b43098e17df9ad49b4da7693 100644 (file)
--- 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 79c5772465f14f1e64a2b962e684b5dfa5338790..53736e52c1dfaa91e00cec2949a396d4354e080f 100644 (file)
--- a/kernel/bpf/preload/bpf_preload_kern.c
+++ b/kernel/bpf/preload/bpf_preload_kern.c
@@ -60,9 +60,12 @@ static int finish(void)
                         &magic, sizeof(magic), &pos);
        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 +83,18 @@ 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 0b35212ffc3d0a60ae796bb98bf2ad7232b541aa..bb7bb3b478abfa5c6dbb81466125858db1f90d5b 100644 (file)
--- a/kernel/usermode_driver.c
+++ b/kernel/usermode_driver.c
@@ -139,13 +139,22 @@ static void umd_cleanup(struct subprocess_info *info)
        struct umd_info *umd_info = info->data;
 
        /* 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;
-       }
+       if (info->retval)
+               umd_cleanup_helper(umd_info);
+}
+
+/**
+ * umd_cleanup_helper - release the resources which were 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