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.
Cc: stable@xxxxxxxxxxxxxxx
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>
---
net/sctp/ipv6.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
index a6dfa86c0201..3b18085e3b10 100644
--- a/net/sctp/ipv6.c
+++ b/net/sctp/ipv6.c
@@ -807,9 +807,10 @@ static void sctp_inet6_skb_msgname(struct sk_buff *skb, char *msgname,
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);
--
2.14.1
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