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Mon, 20 Apr 2020 16:29:29 -0700 (PDT) MIME-Version: 1.0 References: <158741856073.246860.5955712228915579.stgit@chester> <20200420215615.chh4c5ytxumadtt7@madcap2.tricolour.ca> In-Reply-To: <20200420215615.chh4c5ytxumadtt7@madcap2.tricolour.ca> From: Paul Moore Date: Mon, 20 Apr 2020 19:29:18 -0400 Message-ID: Subject: Re: [PATCH] audit: check the length of userspace generated audit records To: Richard Guy Briggs X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-MIME-Autoconverted: from quoted-printable to 8bit by lists01.pubmisc.prod.ext.phx2.redhat.com id 03KNTaQc003660 X-loop: linux-audit@redhat.com Cc: linux-audit@redhat.com X-BeenThere: linux-audit@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: Linux Audit Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-audit-bounces@redhat.com Errors-To: linux-audit-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Mon, Apr 20, 2020 at 5:56 PM Richard Guy Briggs wrote: > On 2020-04-20 17:36, Paul Moore wrote: > > Commit 756125289285 ("audit: always check the netlink payload length > > in audit_receive_msg()") fixed a number of missing message length > > checks, but forgot to check the length of userspace generated audit > > records. The good news is that you need CAP_AUDIT_WRITE to submit > > userspace audit records, which is generally only given to trusted > > processes, so the impact should be limited. > > > > Cc: stable@vger.kernel.org > > Fixes: 756125289285 ("audit: always check the netlink payload length in audit_receive_msg()") > > Reported-by: syzbot+49e69b4d71a420ceda3e@syzkaller.appspotmail.com > > Signed-off-by: Paul Moore > > --- > > kernel/audit.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/kernel/audit.c b/kernel/audit.c > > index b69c8b460341..87f31bf1f0a0 100644 > > --- a/kernel/audit.c > > +++ b/kernel/audit.c > > @@ -1326,6 +1326,9 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh) > > case AUDIT_FIRST_USER_MSG2 ... AUDIT_LAST_USER_MSG2: > > if (!audit_enabled && msg_type != AUDIT_USER_AVC) > > return 0; > > + /* exit early if there isn't at least one character to print */ > > + if (data_len < 2) > > + return -EINVAL; > > Don't we want to issue the record even if the message is empty? If a > len of 1 is passed in, it will properly set str[0] = '\0' and str points > to a location with a null that prints nothing between the single quotes > of "msg=''". So, I think that should be "if (data_len < 1)". > > Am I missing something? I've got no problem with allowing an empty message so long as there is a valid use for such a message. Can anyone think of a valid reason for having an empty userspace generated record? -- paul moore www.paul-moore.com -- Linux-audit mailing list Linux-audit@redhat.com https://www.redhat.com/mailman/listinfo/linux-audit