From: Prince Kumar Maurya <princekumarmaurya06@gmail.com>
To: Christian Brauner <brauner@kernel.org>
Cc: skhan@linuxfoundation.org, viro@zeniv.linux.org.uk,
chenzhongjin@huawei.com, linux-kernel@vger.kernel.org,
linux-kernel-mentees@lists.linuxfoundation.org,
syzkaller-bugs@googlegroups.com, linux-fsdevel@vger.kernel.org,
syzbot+aad58150cbc64ba41bdc@syzkaller.appspotmail.com
Subject: Re: [PATCH v3] fs/sysv: Null check to prevent null-ptr-deref bug
Date: Tue, 30 May 2023 07:59:16 -0700 [thread overview]
Message-ID: <CAF0B0eKxMf7-uzgRJcWsWW6hgxP25bPG8U9nF0by7mSNvhZmbQ@mail.gmail.com> (raw)
In-Reply-To: <20230530-zenit-radeln-06417ce5fe85@brauner>
On Tue, May 30, 2023 at 1:26 AM Christian Brauner <brauner@kernel.org> wrote:
>
> On Sun, May 28, 2023 at 11:44:22AM -0700, Prince Kumar Maurya wrote:
> > sb_getblk(inode->i_sb, parent) return a null ptr and taking lock on
> > that leads to the null-ptr-deref bug.
> >
> > Reported-by: syzbot+aad58150cbc64ba41bdc@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=aad58150cbc64ba41bdc
> > Signed-off-by: Prince Kumar Maurya <princekumarmaurya06@gmail.com>
> > ---
> > Change since v2: Updated subject and added Reported-by and closes tags.
> >
> > fs/sysv/itree.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/fs/sysv/itree.c b/fs/sysv/itree.c
> > index b22764fe669c..3a6b66e719fd 100644
> > --- a/fs/sysv/itree.c
> > +++ b/fs/sysv/itree.c
> > @@ -145,6 +145,8 @@ static int alloc_branch(struct inode *inode,
> > */
> > parent = block_to_cpu(SYSV_SB(inode->i_sb), branch[n-1].key);
> > bh = sb_getblk(inode->i_sb, parent);
> > + if (!bh)
> > + break;
>
> When you break here you'll hit:
>
> /* Allocation failed, free what we already allocated */
> for (i = 1; i < n; i++)
> bforget(branch[i].bh);
> for (i = 0; i < n; i++)
> sysv_free_block(inode->i_sb, branch[i].key);
>
> below. The cleanup paths were coded in the assumption that sb_getblk()
> can't fail. So bforget() can assume that branch[i].bh has been allocated
> and set up. So that bforget(branch[i].bh) is your next pending NULL
> deref afaict.
I doubt that would happen. There is a break above as well, before we do
sb_getblk().
/* Allocate the next block */
branch[n].key = sysv_new_block(inode->i_sb);
if (!branch[n].key)
break;
The clean up code path runs till i is less than n not equal to n which
would have caused the problem.
next prev parent reply other threads:[~2023-05-30 15:00 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-22 22:36 [syzbot] [fs?] KASAN: null-ptr-deref Write in get_block (2) syzbot
2023-05-28 1:25 ` [PATCH] Null check to prevent null-ptr-deref bug Prince Kumar Maurya
2023-05-28 6:58 ` Greg KH
2023-05-28 16:44 ` Prince Kumar Maurya
2023-05-28 16:46 ` Greg KH
2023-05-28 17:35 ` Prince Kumar Maurya
2023-05-28 17:51 ` Greg KH
2023-05-28 17:52 ` Greg KH
2023-05-28 18:44 ` [PATCH v3] fs/sysv: " Prince Kumar Maurya
2023-05-30 8:26 ` Christian Brauner
2023-05-30 14:59 ` Prince Kumar Maurya [this message]
2023-05-30 15:54 ` Christian Brauner
2023-05-31 1:31 ` [PATCH v4] " Prince Kumar Maurya
2023-06-01 7:55 ` Christian Brauner
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