From: Laszlo Ersek <lersek@redhat.com>
Date: Mon, 31 Jul 2023 18:42:37 +0200
Subject: net: tap_open(): set sk_uid from current_fsuid()
Git-commit: 5c9241f3ceab3257abe2923a59950db0dc8bb737
Patch-mainline: v6.5-rc5
References: CVE-2023-4194 bsc#1214019
Commit 66b2c338adce initializes the "sk_uid" field in the protocol socket
(struct sock) from the "/dev/tapX" device node's owner UID. Per original
commit 86741ec25462 ("net: core: Add a UID field to struct sock.",
2016-11-04), that's wrong: the idea is to cache the UID of the userspace
process that creates the socket. Commit 86741ec25462 mentions socket() and
accept(); with "tap", the action that creates the socket is
open("/dev/tapX").
Therefore the device node's owner UID is irrelevant. In most cases,
"/dev/tapX" will be owned by root, so in practice, commit 66b2c338adce has
no observable effect:
- before, "sk_uid" would be zero, due to undefined behavior
(CVE-2023-1076),
- after, "sk_uid" would be zero, due to "/dev/tapX" being owned by root.
What matters is the (fs)UID of the process performing the open(), so cache
that in "sk_uid".
Cc: Eric Dumazet <edumazet@google.com>
Cc: Lorenzo Colitti <lorenzo@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Pietro Borrello <borrello@diag.uniroma1.it>
Cc: netdev@vger.kernel.org
Cc: stable@vger.kernel.org
Fixes: 66b2c338adce ("tap: tap_open(): correctly initialize socket uid")
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2173435
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Miroslav Franc <mfranc@suse.cz>
---
drivers/net/tap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 9137fb8c1c42..49d1d6acf95e 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -534,7 +534,7 @@ static int tap_open(struct inode *inode, struct file *file)
q->sock.state = SS_CONNECTED;
q->sock.file = file;
q->sock.ops = &tap_socket_ops;
- sock_init_data_uid(&q->sock, &q->sk, inode->i_uid);
+ sock_init_data_uid(&q->sock, &q->sk, current_fsuid());
q->sk.sk_write_space = tap_sock_write_space;
q->sk.sk_destruct = tap_sock_destruct;
q->flags = IFF_VNET_HDR | IFF_NO_PI | IFF_TAP;