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 4.13-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

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-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Tue Nov 21 13:07:20 CET 2017

From: "Eric W. Biederman" ebiederm@xmission.com 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@xmission.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@google.com Tested-by: Alexander Potapenko glider@google.com Signed-off-by: "Eric W. Biederman" ebiederm@xmission.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/sctp/ipv6.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/net/sctp/ipv6.c +++ b/net/sctp/ipv6.c @@ -807,9 +807,10 @@ 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@xmission.com are

queue-4.13/net-sctp-always-set-scope_id-in-sctp_inet6_skb_msgname.patch