From: Laszlo Ersek <lersek@redhat.com>
Date: Mon, 31 Jul 2023 18:42:36 +0200
Subject: net: tun_chr_open(): set sk_uid from current_fsuid()
Git-commit: 9bc3047374d5bec163e83e743709e23753376f0c
Patch-mainline: v6.5-rc5
References: CVE-2023-4194 bsc#1214019
Commit a096ccca6e50 initializes the "sk_uid" field in the protocol socket
(struct sock) from the "/dev/net/tun" 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 "tun", the action that creates the socket is
open("/dev/net/tun").
Therefore the device node's owner UID is irrelevant. In most cases,
"/dev/net/tun" will be owned by root, so in practice, commit a096ccca6e50
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/net/tun" 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: a096ccca6e50 ("tun: tun_chr_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/tun.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index d75456adc62a..25f0191df00b 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -3469,7 +3469,7 @@ static int tun_chr_open(struct inode *inode, struct file * file)
tfile->socket.file = file;
tfile->socket.ops = &tun_socket_ops;
- sock_init_data_uid(&tfile->socket, &tfile->sk, inode->i_uid);
+ sock_init_data_uid(&tfile->socket, &tfile->sk, current_fsuid());
tfile->sk.sk_write_space = tun_sock_write_space;
tfile->sk.sk_sndbuf = INT_MAX;