2021-03-15 08:17:08

by Zhang, Qiang

Subject: [PATCH v2] bpf: Fix memory leak in copy_process()

From: Zqiang <[email protected]>

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: [email protected]
Signed-off-by: Zqiang <[email protected]>
---
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

2021-03-15 08:35:48

by Daniel Borkmann

Subject: Re: [PATCH v2] bpf: Fix memory leak in copy_process()

On 3/15/21 9:18 AM, [email protected] wrote:
> From: Zqiang <[email protected]>

Hello Zqiang, please resend this patch with [email protected] in Cc, so it
actually reaches the rest of BPF community for review, thanks!

> 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: [email protected]
> Signed-off-by: Zqiang <[email protected]>
> ---
> v1->v2:
> Judge whether the pointer variable tgid is valid.