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 17:28:15 +0300 Message-ID: <20200723142814.GQ2549@kadam> References: <20200722151901.350003-1-yepeilin.cs@gmail.com> 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=sC9ikgxCdAId2FjwuAiIMWAdpmWMyGPubI1xPl1Ci74=; b=SIdFDBZUeQfxAJn2svTXpXwgZNNciCu1DUh7fq6b8KCb49Zf7f6z/Y1T2E7NA/UNpYvP pIIEYqWYl+/apLvEGx4+sWp+8ORDdOkk2UhKeoS8Gcdcc75aRZrU+TvuE6wEgfiCYHvo UegwsySFybvAMf7PJ1CKN1GY58g4WuoC6FwR9twka5FQBzQoUetCnCJjpDWtXltXJ5PH LFhdCFw1kAWuqUFY1FN+WvAWOlqt0Gi8csmGpUiEREPK1IiQKvjVqpk6R8Uexvgeb+Fx 3Bobs8VVJmID+kUba8DZXsSbVpHiKHQgLqUH7vOG6rOPI3LOGxVEQ1bfryMxdh/bRdxN NA== Content-Disposition: inline In-Reply-To: <20200722151901.350003-1-yepeilin.cs@gmail.com> Sender: linux-hams-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 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. regards, dan carpenter