In the Linux kernel, the following vulnerability has been resolved:
net: openvswitch: validate transport header presence in set_ipv6_addr
When executing IPv6 address rewrite actions on IPv6 fragments,
set_ipv6_addr() calls update_ipv6_checksum(). If parse_ipv6hdr()
processes a non-first IPv6 fragment, it sets key->ip.proto to
NEXTHDR_FRAGMENT and returns early without calling
skb_set_transport_header().
update_ipv6_checksum() unconditionally evaluates skb_transport_offset()
on entry before checking l4_proto. Because skb->transport_header is
uninitialized, this triggers a warning under CONFIG_DEBUG_NET=y although
it is completely harmless.
Fix this by returning early in update_ipv6_checksum() if l4_proto is
NEXTHDR_FRAGMENT. This avoids reading the uninitialized transport offset
for fragments while preserving the debug warning for any other protocol
where the transport header is unexpectedly missing.
See the syzbot trace:
!skb_transport_header_was_set(skb)
WARNING: ./include/linux/skbuff.h:3075 at skb_transport_header include/linux/skbuff.h:3075 [inline], CPU#1: syz-executor463/5635
WARNING: ./include/linux/skbuff.h:3075 at skb_transport_offset include/linux/skbuff.h:3250 [inline], CPU#1: syz-executor463/5635
WARNING: ./include/linux/skbuff.h:3075 at update_ipv6_checksum net/openvswitch/actions.c:361 [inline], CPU#1: syz-executor463/5635
WARNING: ./include/linux/skbuff.h:3075 at set_ipv6_addr+0x462/0x660 net/openvswitch/actions.c:399, CPU#1: syz-executor463/5635
[...]
RIP: 0010:skb_transport_header include/linux/skbuff.h:3075 [inline]
RIP: 0010:skb_transport_offset include/linux/skbuff.h:3250 [inline]
RIP: 0010:update_ipv6_checksum net/openvswitch/actions.c:361 [inline]
RIP: 0010:set_ipv6_addr+0x462/0x660 net/openvswitch/actions.c:399
[...]
Call Trace:
Unknown