ipv6_find_hdr() walks the extension header chain, skipping each header by
the length that header itself declares. ipv6_optlen() returns up to 2048,
and the skip is never checked against skb->len, so the offset stored in
*offset can point past the end of the packet.
openvswitch installs that offset as the transport header, and
update_ipv6_checksum() then reads and writes the transport checksum field
out of bounds:
BUG: KASAN: slab-use-after-free in inet_proto_csum_replace16+0x445/0x470
Read of size 2 at addr ffff88810b754b06 by task ovs_ipv6_oob/629
CPU: 4 UID: 1000 PID: 629 Comm: ovs_ipv6_oob Tainted: G N 7.3.0-rc3+ #348
Call Trace:
inet_proto_csum_replace16+0x445/0x470
set_ipv6_addr+0x3dd/0x460
do_execute_actions+0x6a3d/0x7c40
ovs_execute_actions+0xfd/0x480
ovs_packet_cmd_execute+0xc38/0xf20
genl_rcv_msg+0x59e/0x870
netlink_rcv_skb+0x18b/0x450
genl_rcv+0x2d/0x40
netlink_unicast+0x6bc/0xa20
The buggy address belongs to the object at ffff88810b754980
which belongs to the cache skbuff_small_head of size 704
The buggy address is located 390 bytes inside of
freed 704-byte region [ffff88810b754980, ffff88810b754c40)
Other callers use that offset too, so bound it here rather than in one
caller.
Reject a header whose declared length does not fit in the packet.
ipv6_find_hdr() already fails with -EBADMSG on a malformed chain, so this
adds no new failure mode.
Fixes: f8f626754ebe ("ipv6: Move ipv6_find_hdr() out of Netfilter code.")
Suggested-by: Ilya Maximets <[email protected]>
Suggested-by: Eric Dumazet <[email protected]>
Cc: [email protected]
Assisted-by: LLM
Signed-off-by: Norbert Szetei <[email protected]>
---
v2:
- fix ipv6_find_hdr() instead of the openvswitch caller, per the review
of v1
- dropped the openvswitch change
- retitled
v1:
https://lore.kernel.org/netdev/[email protected]/
Reproducer available on request.
net/ipv6/exthdrs_core.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/net/ipv6/exthdrs_core.c b/net/ipv6/exthdrs_core.c
index 9d06d487e8b1..4a9748338cf4 100644
--- a/net/ipv6/exthdrs_core.c
+++ b/net/ipv6/exthdrs_core.c
@@ -278,6 +278,9 @@ int ipv6_find_hdr(const struct sk_buff *skb, unsigned int
*offset,
hdrlen = ipv6_optlen(hp);
if (!found) {
+ if (skb->len - start < hdrlen)
+ return -EBADMSG;
+
nexthdr = hp->nexthdr;
start += hdrlen;
}
--
2.55.0
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