3.16.54-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> commit 7c8a61d9ee1df0fb4747879fa67a99614eb62fec upstream. 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> [bwh: Backported to 3.16: - Adjust context - Add braces] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- --- a/net/sctp/ipv6.c +++ b/net/sctp/ipv6.c @@ -787,6 +787,8 @@ 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; } }