linux-kernel - Re: [PATCH] fix: general protection fault in iter_file_splice

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Message-ID: <20241104120615.ggsn7g2gblw73c5l@quack3>
Date: Mon, 4 Nov 2024 13:06:15 +0100
From: Jan Kara <jack@...e.cz>
To: Daniel Yang <danielyangkang@...il.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	"open list:FILESYSTEMS (VFS and infrastructure)" <linux-fsdevel@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	syzbot+d2125fcb6aa8c4276fd2@...kaller.appspotmail.com
Subject: Re: [PATCH] fix: general protection fault in iter_file_splice_write

On Mon 04-11-24 00:42:39, Daniel Yang wrote:
> The function iter_file_splice_write() calls pipe_buf_release() which has
> a nullptr dereference in ops->release. Add check for buf->ops not null
> before calling pipe_buf_release().
> 
> Signed-off-by: Daniel Yang <danielyangkang@...il.com>
> Reported-by: syzbot+d2125fcb6aa8c4276fd2@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=d2125fcb6aa8c4276fd2
> Fixes: 2df86547b23d ("netfs: Cut over to using new writeback code")
> ---
>  fs/splice.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/splice.c b/fs/splice.c
> index 06232d7e5..b8c503e47 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -756,7 +756,8 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
>  			if (ret >= buf->len) {
>  				ret -= buf->len;
>  				buf->len = 0;
> -				pipe_buf_release(pipe, buf);
> +				if (buf->ops)
> +					pipe_buf_release(pipe, buf);

Umm, already released pipe buf? How would it get here? We have filled the
buffers shortly before so IMHO it indicates some deeper problem. Can you
please explain a bit more?

								Honza


>  				tail++;
>  				pipe->tail = tail;
>  				if (pipe->files)
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR