[PATCH 5.4 065/108] sctp: update active_key for asoc when old key is being replaced

Greg Kroah-Hartman
2021-07-26T16:14:12Z

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

[ Upstream commit 58acd10092268831e49de279446c314727101292 ]

syzbot reported a call trace:

BUG: KASAN: use-after-free in sctp_auth_shkey_hold+0x22/0xa0 net/sctp/auth.c:112
Call Trace:
sctp_auth_shkey_hold+0x22/0xa0 net/sctp/auth.c:112
sctp_set_owner_w net/sctp/socket.c:131 [inline]
sctp_sendmsg_to_asoc+0x152e/0x2180 net/sctp/socket.c:1865
sctp_sendmsg+0x103b/0x1d30 net/sctp/socket.c:2027
inet_sendmsg+0x99/0xe0 net/ipv4/af_inet.c:821
sock_sendmsg_nosec net/socket.c:703 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:723

This is an use-after-free issue caused by not updating asoc->shkey after
it was replaced in the key list asoc->endpoint_shared_keys, and the old
key was freed.

This patch is to fix by also updating active_key for asoc when old key is
being replaced with a new one. Note that this issue doesn't exist in
sctp_auth_del_key_id(), as it's not allowed to delete the active_key
from the asoc.

Fixes: 1b1e0bc99474 ("sctp: add refcnt support for sh_key")
Reported-by: syzbot+b774577370208727d12b@syzkaller.appspotmail.com
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sctp/auth.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/net/sctp/auth.c b/net/sctp/auth.c
index 1d898ee4018c..7eced1e523a5 100644
--- a/net/sctp/auth.c
+++ b/net/sctp/auth.c
@@ -866,6 +866,8 @@ int sctp_auth_set_key(struct sctp_endpoint *ep,
if (replace) {
list_del_init(&shkey->key_list);
sctp_auth_shkey_release(shkey);
+ if (asoc && asoc->active_key_id == auth_key->sca_keynumber)
+ sctp_auth_asoc_init_active_key(asoc, GFP_KERNEL);
}
list_add(&cur_key->key_list, sh_keys);

--
2.30.2