From: Eric W. Biederman Date: Thu, 16 Nov 2017 04:17:48 +0000 (-0600) Subject: net/sctp: Always set scope_id in sctp_inet6_skb_msgname X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=753cbba3bd5ce44baf645ab4289d99e22ef13d44;p=pandora-kernel.git net/sctp: Always set scope_id in sctp_inet6_skb_msgname 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 Tested-by: Alexander Potapenko Signed-off-by: "Eric W. Biederman" Signed-off-by: David S. Miller [bwh: Backported to 3.2: - Adjust context - Add braces] Signed-off-by: Ben Hutchings --- Reading git-diff-tree failed