From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Carpenter Subject: Re: [Linux-kernel-mentees] [PATCH net] AX.25: Fix out-of-bounds read in ax25_connect() Date: Thu, 23 Jul 2020 18:50:58 +0300 Message-ID: <20200723155057.GS2549@kadam> References: <20200722151901.350003-1-yepeilin.cs@gmail.com> <20200723142814.GQ2549@kadam> <20200723151355.GA412829@PWN> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to; s=corp-2020-01-29; bh=YEJKJVrh9zyoniRPLQ5+w7YtIh1urn01ae/6cECcoOs=; b=rF4NclcxAYyJyD6H+rKmY9tFMDz/axd5uFwaZWuGC+0r5tVShxd5zHntlPmOzdcKCA22 B3Bji8s5s0NtXMqZgwa6E0ZY05ClKySatJOFrEHtW5xIo590eHOmED9M/CiwH/o89etj 603PUT4xfNNAyg1tO6dASXYP1O/UpkyRySMvhDoW1HD1c3nmSHGreY1PywGMj2R6kMA/ lajZOBoBX3MaU/xChX8hsbwjiQPE1jkU6CL1+kunQn/A4bUuWrA4rys6AZ7WWoK9H7Rn oJtAdiI9Sj8pqh3OAio3L6x2nx4YLws4H31pmgvKToWJCqwPg//JFk330v33Za1Sea+P Zg== Content-Disposition: inline In-Reply-To: <20200723151355.GA412829@PWN> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Peilin Ye Cc: Joerg Reuter , Ralf Baechle , Greg Kroah-Hartman , syzkaller-bugs@googlegroups.com, linux-kernel-mentees@lists.linuxfoundation.org, "David S . Miller" , Jakub Kicinski , linux-hams@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org On Thu, Jul 23, 2020 at 11:13:55AM -0400, Peilin Ye wrote: > On Thu, Jul 23, 2020 at 05:28:15PM +0300, Dan Carpenter wrote: > > On Wed, Jul 22, 2020 at 11:19:01AM -0400, Peilin Ye wrote: > > > Checks on `addr_len` and `fsa->fsa_ax25.sax25_ndigis` are insufficient. > > > ax25_connect() can go out of bounds when `fsa->fsa_ax25.sax25_ndigis` > > > equals to 7 or 8. Fix it. > > > > > > This issue has been reported as a KMSAN uninit-value bug, because in such > > > a case, ax25_connect() reaches into the uninitialized portion of the > > > `struct sockaddr_storage` statically allocated in __sys_connect(). > > > > > > It is safe to remove `fsa->fsa_ax25.sax25_ndigis > AX25_MAX_DIGIS` because > > > `addr_len` is guaranteed to be less than or equal to > > > `sizeof(struct full_sockaddr_ax25)`. > > > > > > Reported-by: syzbot+c82752228ed975b0a623@syzkaller.appspotmail.com > > > Link: https://syzkaller.appspot.com/bug?id=55ef9d629f3b3d7d70b69558015b63b48d01af66 > > > Signed-off-by: Peilin Ye > > > --- > > > net/ax25/af_ax25.c | 4 +++- > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c > > > index fd91cd34f25e..ef5bf116157a 100644 > > > --- a/net/ax25/af_ax25.c > > > +++ b/net/ax25/af_ax25.c > > > @@ -1187,7 +1187,9 @@ static int __must_check ax25_connect(struct socket *sock, > > > if (addr_len > sizeof(struct sockaddr_ax25) && > > > fsa->fsa_ax25.sax25_ndigis != 0) { > > > /* Valid number of digipeaters ? */ > > > - if (fsa->fsa_ax25.sax25_ndigis < 1 || fsa->fsa_ax25.sax25_ndigis > AX25_MAX_DIGIS) { > > > + if (fsa->fsa_ax25.sax25_ndigis < 1 || > > > + addr_len < sizeof(struct sockaddr_ax25) + > > > + sizeof(ax25_address) * fsa->fsa_ax25.sax25_ndigis) { > > > > The "sizeof(ax25_address) * fsa->fsa_ax25.sax25_ndigis" can have an > > integer overflow so you still need the > > "fsa->fsa_ax25.sax25_ndigis > AX25_MAX_DIGIS" check. > > Thank you for fixing this up! I did some math but I didn't think of > that. Will be more careful when removing things. No problem. You had the right approach to look for ways to clean things up. Your patches make me happy because you're trying to fix important bugs. regards, dan carpenter