linux-kernel - [PATCH 4.4 08/16] net/sctp: Always set scope_id in sctp_inet6_skb

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20171122101111.171385746@linuxfoundation.org>
Date:   Wed, 22 Nov 2017 11:12:01 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Alexander Potapenko <glider@...gle.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.4 08/16] net/sctp: Always set scope_id in sctp_inet6_skb_msgname

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Eric W. Biederman" <ebiederm@...ssion.com>

[ Upstream commit 7c8a61d9ee1df0fb4747879fa67a99614eb62fec ]

Alexandar Potapenko while testing the kernel with KMSAN and syzkaller
discovered that in some configurations sctp would leak 4 bytes of
kernel stack.

Working with his reproducer I discovered that those 4 bytes that
are leaked is the scope id of an ipv6 address returned by recvmsg.

With a little code inspection and a shrewd guess I discovered that
sctp_inet6_skb_msgname only initializes the scope_id field for link
local ipv6 addresses to the interface index the link local address
pertains to instead of initializing the scope_id field for all ipv6
addresses.

That is almost reasonable as scope_id's are meaniningful only for link
local addresses.  Set the scope_id in all other cases to 0 which is
not a valid interface index to make it clear there is nothing useful
in the scope_id field.

There should be no danger of breaking userspace as the stack leak
guaranteed that previously meaningless random data was being returned.

Fixes: 372f525b495c ("SCTP:  Resync with LKSCTP tree.")
History-tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Reported-by: Alexander Potapenko <glider@...gle.com>
Tested-by: Alexander Potapenko <glider@...gle.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/sctp/ipv6.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/net/sctp/ipv6.c
+++ b/net/sctp/ipv6.c
@@ -806,6 +806,8 @@ static void sctp_inet6_skb_msgname(struc
 		if (ipv6_addr_type(&addr->v6.sin6_addr) & IPV6_ADDR_LINKLOCAL) {
 			struct sctp_ulpevent *ev = sctp_skb2event(skb);
 			addr->v6.sin6_scope_id = ev->iif;
+		} else {
+			addr->v6.sin6_scope_id = 0;
 		}
 	}