linux-kernel - 回复: [PATCH v2] bpf: Fix memory leak in copy

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Date:   Tue, 16 Mar 2021 11:29:36 +0000
From:   "Zhang, Qiang" <Qiang.Zhang@...driver.com>
To:     "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "andrii@...nel.org" <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        "kpsingh@...nel.org" <kpsingh@...nel.org>,
        "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>
CC:     "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "syzbot+44908bb56d2bfe56b28e@...kaller.appspotmail.com" 
        <syzbot+44908bb56d2bfe56b28e@...kaller.appspotmail.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: 回复: [PATCH v2] bpf: Fix memory leak in copy_process()

Hello Alexei Starovoitov Daniel Borkmann
Please  review this patch.

Thanks
Qiang

________________________________________
发件人: Zhang, Qiang <qiang.zhang@...driver.com>
发送时间: 2021年3月15日 16:53
收件人: ast@...nel.org; daniel@...earbox.net; andrii@...nel.org
抄送: dvyukov@...gle.com; linux-kernel@...r.kernel.org; syzbot+44908bb56d2bfe56b28e@...kaller.appspotmail.com; bpf@...r.kernel.org; Zhang, Qiang
主题: [PATCH v2] bpf: Fix memory leak in copy_process()

From: Zqiang <qiang.zhang@...driver.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@...kaller.appspotmail.com
Signed-off-by: Zqiang <qiang.zhang@...driver.com>
---
 v1->v2:
 Judge whether the pointer variable tgid is valid.

 kernel/bpf/preload/bpf_preload_kern.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/preload/bpf_preload_kern.c b/kernel/bpf/preload/bpf_preload_kern.c
index 79c5772465f1..5009875f01d3 100644
--- a/kernel/bpf/preload/bpf_preload_kern.c
+++ b/kernel/bpf/preload/bpf_preload_kern.c
@@ -4,6 +4,7 @@
 #include <linux/module.h>
 #include <linux/pid.h>
 #include <linux/fs.h>
+#include <linux/file.h>
 #include <linux/sched/signal.h>
 #include "bpf_preload.h"

@@ -20,6 +21,14 @@ static struct bpf_preload_ops umd_ops = {
        .owner = THIS_MODULE,
 };

+static void bpf_preload_umh_cleanup(struct umd_info *info)
+{
+       fput(info->pipe_to_umh);
+       fput(info->pipe_from_umh);
+       put_pid(info->tgid);
+       info->tgid = NULL;
+}
+
 static int preload(struct bpf_preload_info *obj)
 {
        int magic = BPF_PRELOAD_START;
@@ -61,8 +70,10 @@ 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));
+               bpf_preload_umh_cleanup(&umd_ops.info);
+       }
        return 0;
 }

@@ -80,10 +91,15 @@ 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));
+               bpf_preload_umh_cleanup(&umd_ops.info);
+       }
        umd_unload_blob(&umd_ops.info);
 }
 late_initcall(load_umd);
--
2.17.1