linux-kernel - Re: general protection fault in fuse_ctl_remove

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Date:   Thu, 31 May 2018 16:27:58 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     syzbot <syzbot+32c236387d66c4516827@...kaller.appspotmail.com>,
        syzkaller-bugs@...glegroups.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: general protection fault in fuse_ctl_remove_conn

On Sat, Apr 28, 2018 at 4:29 AM, Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
> From 9f41081f8bd6762a6f629e5e23e6d07a62bba69c Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Date: Sat, 28 Apr 2018 11:24:09 +0900
> Subject: [PATCH] fuse: don't keep inode-less dentry at fuse_ctl_add_dentry().
>
> syzbot is reporting NULL pointer dereference at fuse_ctl_remove_conn() [1].
> Since fc->ctl_ndents is incremented by fuse_ctl_add_conn() when new_inode()
> failed, fuse_ctl_remove_conn() reaches an inode-less dentry and tries to
> clear d_inode(dentry)->i_private field. Fix this by calling dput() rather
> than incrementing fc->ctl_ndents when new_inode() failed.
>
> [1] https://syzkaller.appspot.com/bug?id=f396d863067238959c91c0b7cfc10b163638cac6

Slightly different fix pushed to:

  git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git for-next

Thanks,
Miklos