This is a note to let you know that I've just added the patch titled net/sctp: Always set scope_id in sctp_inet6_skb_msgname to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-sctp-always-set-scope_id-in-sctp_inet6_skb_msgname.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Tue Nov 21 13:08:13 CET 2017 From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Date: Wed, 15 Nov 2017 22:17:48 -0600 Subject: net/sctp: Always set scope_id in sctp_inet6_skb_msgname From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> [ 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@xxxxxxxxxx> Tested-by: Alexander Potapenko <glider@xxxxxxxxxx> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/sctp/ipv6.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/net/sctp/ipv6.c +++ b/net/sctp/ipv6.c @@ -806,9 +806,10 @@ static void sctp_inet6_skb_msgname(struc addr->v6.sin6_flowinfo = 0; addr->v6.sin6_port = sh->source; addr->v6.sin6_addr = ipv6_hdr(skb)->saddr; - if (ipv6_addr_type(&addr->v6.sin6_addr) & IPV6_ADDR_LINKLOCAL) { + if (ipv6_addr_type(&addr->v6.sin6_addr) & IPV6_ADDR_LINKLOCAL) addr->v6.sin6_scope_id = sctp_v6_skb_iif(skb); - } + else + addr->v6.sin6_scope_id = 0; } *addr_len = sctp_v6_addr_to_user(sctp_sk(skb->sk), addr); Patches currently in stable-queue which might be from ebiederm@xxxxxxxxxxxx are queue-4.9/net-sctp-always-set-scope_id-in-sctp_inet6_skb_msgname.patch