From 9bc3047374d5bec163e83e743709e23753376f0c Mon Sep 17 00:00:00 2001 From: Laszlo Ersek Date: Mon, 31 Jul 2023 18:42:36 +0200 Subject: [PATCH] net: tun_chr_open(): set sk_uid from current_fsuid() 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 Cc: Lorenzo Colitti Cc: Paolo Abeni Cc: Pietro Borrello 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 Signed-off-by: David S. Miller --- 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 d75456a..25f0191 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; -- 2.7.4