[PATCH 5.4 117/155] xfrm: add the missing verify_sec_ctx_len check in xfrm_add_acquire

Greg Kroah-Hartman
2020-03-31T09:16:57Z

From: Xin Long <lucien.xin@gmail.com>

commit a1a7e3a36e01ca6e67014f8cf673cb8e47be5550 upstream.

Without doing verify_sec_ctx_len() check in xfrm_add_acquire(), it may be
out-of-bounds to access uctx->ctx_str with uctx->ctx_len, as noticed by
syz:

BUG: KASAN: slab-out-of-bounds in selinux_xfrm_alloc_user+0x237/0x430
Read of size 768 at addr ffff8880123be9b4 by task syz-executor.1/11650

Call Trace:
dump_stack+0xe8/0x16e
print_address_description.cold.3+0x9/0x23b
kasan_report.cold.4+0x64/0x95
memcpy+0x1f/0x50
selinux_xfrm_alloc_user+0x237/0x430
security_xfrm_policy_alloc+0x5c/0xb0
xfrm_policy_construct+0x2b1/0x650
xfrm_add_acquire+0x21d/0xa10
xfrm_user_rcv_msg+0x431/0x6f0
netlink_rcv_skb+0x15a/0x410
xfrm_netlink_rcv+0x6d/0x90
netlink_unicast+0x50e/0x6a0
netlink_sendmsg+0x8ae/0xd40
sock_sendmsg+0x133/0x170
___sys_sendmsg+0x834/0x9a0
__sys_sendmsg+0x100/0x1e0
do_syscall_64+0xe5/0x660
entry_SYSCALL_64_after_hwframe+0x6a/0xdf

So fix it by adding the missing verify_sec_ctx_len check there.

Fixes: 980ebd25794f ("[IPSEC]: Sync series - acquire insert")
Reported-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/xfrm/xfrm_user.c | 3 +++
1 file changed, 3 insertions(+)

--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -2276,6 +2276,9 @@ static int xfrm_add_acquire(struct sk_bu
err = verify_newpolicy_info(&ua->policy);
if (err)
goto free_state;
+ err = verify_sec_ctx_len(attrs);
+ if (err)
+ goto free_state;

/* build an XP */
xp = xfrm_policy_construct(net, &ua->policy, attrs, &err);