4.9-stable review patch. If anyone has any objections, please let me know.
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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 @@ -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);