2022-10-17 10:10:26

by Hoi Pok Wu

Subject: [PATCH] fs: f2fs: fix kernel discard_thread NULL dereference

Pointer discard_thread is pointing to nowhere, using IS_ERR prevents the
situation. IS_ERR also seen being used throughout the file.

Link: https://syzkaller.appspot.com/bug?id=9499bc6574cea5940e48199c2fd0732d9b11e5e1
Reported-by: [email protected]
Signed-off-by: Hoi Pok Wu <[email protected]>
---
fs/f2fs/segment.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index acf3d3fa4363..79978b7206b5 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1634,7 +1634,8 @@ void f2fs_stop_discard_thread(struct f2fs_sb_info *sbi)
struct task_struct *discard_thread = dcc->f2fs_issue_discard;

dcc->f2fs_issue_discard = NULL;
- kthread_stop(discard_thread);
+ if (!IS_ERR(discard_thread))
+ kthread_stop(discard_thread);
}
}

--
2.38.0

2022-10-17 12:36:45

by Chao Yu

Subject: Re: [PATCH] fs: f2fs: fix kernel discard_thread NULL dereference

On 2022/10/17 18:04, Hoi Pok Wu wrote:
> Pointer discard_thread is pointing to nowhere, using IS_ERR prevents the
> situation. IS_ERR also seen being used throughout the file.

I guess below patch can fix this issue from root cause?

https://lore.kernel.org/linux-f2fs-devel/[email protected]/T/#u

Thanks,

>
> Link: https://syzkaller.appspot.com/bug?id=9499bc6574cea5940e48199c2fd0732d9b11e5e1
> Reported-by: [email protected]
> Signed-off-by: Hoi Pok Wu <[email protected]>
> ---
> fs/f2fs/segment.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index acf3d3fa4363..79978b7206b5 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1634,7 +1634,8 @@ void f2fs_stop_discard_thread(struct f2fs_sb_info *sbi)
> struct task_struct *discard_thread = dcc->f2fs_issue_discard;
>
> dcc->f2fs_issue_discard = NULL;
> - kthread_stop(discard_thread);
> + if (!IS_ERR(discard_thread))
> + kthread_stop(discard_thread);
> }
> }
>