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