On 10/1/26 1:15 PM, Ilya Maximets wrote:
On 10/1/26 10:52 AM, Fernando Fernandez Mancera wrote:
When executing IPv6 address rewrite actions on IPv6 fragments,
set_ipv6_addr() might attempt to recalculate the L4 header checksum
calling skb_transport_header() with an uninitialized transport header.
This can potentially lead to a OOB write.
Not really. later fragments have l4_proto set to NEXTHDR_FRAGMENT
and so no writes will be performed. See parse_ipv6hdr().
Oh, I didn't notice that. In that case, this is harmless. I will update
the commit message, thanks!
A warning is triggered with DEBUG_NET=y.
Yeah, while the value is not actually used to access the packet data,
the skbuff core generates a warning on read.
Fix this by recalculating the checksum only if there is a valid
transport header in the skb. Otherwise, assume this is a fragment and
skip it.
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:
<TASK>
set_ipv6 net/openvswitch/actions.c:531 [inline]
do_execute_actions+0x557e/0x8600 net/openvswitch/actions.c:1366
ovs_execute_actions+0xde/0x520 net/openvswitch/actions.c:1592
ovs_packet_cmd_execute+0xb4f/0xf10 net/openvswitch/datapath.c:705
genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114
genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2572
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast+0x7bd/0x940 net/netlink/af_netlink.c:1361
netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1916
sock_sendmsg_nosec+0x14e/0x190 net/socket.c:800
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=4cc63fcfb3845e149969
Fixes: 3fdbd1ce11e5 ("openvswitch: add ipv6 'set' action")
Signed-off-by: Fernando Fernandez Mancera <[email protected]>
---
net/openvswitch/actions.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index dc5ff859f114..a14668565ec4 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -395,7 +395,7 @@ static void set_ipv6_addr(struct sk_buff *skb, u8 l4_proto,
__be32 addr[4], const __be32 new_addr[4],
bool recalculate_csum)
{
- if (recalculate_csum)
+ if (recalculate_csum && skb_transport_header_was_set(skb))
update_ipv6_checksum(skb, l4_proto, addr, new_addr);
I'd suggest moving the check into update_ipv6_checksum() and maybe add
a small comment that the check is only to avoid warning on reading the
offset that wasn't set, offset must always be set for any l4_proto for
which the checksum is actually getting updated.
Will do that. Thanks Ilya.
Best regards, Ilya Maximets.
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