From 51b8aea7abdeb522e5450c246912b6f4a491e1c8 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Wed, 15 Nov 2017 22:17:48 -0600 Subject: net/sctp: Always set scope_id in sctp_inet6_skb_msgname [ 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 Tested-by: Alexander Potapenko Signed-off-by: "Eric W. Biederman" Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/sctp/ipv6.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c index e33e9bd4ed5a..8a61ccc37e12 100644 --- a/net/sctp/ipv6.c +++ b/net/sctp/ipv6.c @@ -806,6 +806,8 @@ static void sctp_inet6_skb_msgname(struct sk_buff *skb, char *msgname, 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; } } -- cgit v1.2.3