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net: tun_chr_open(): set sk_uid from current_fsuid()

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commit 9bc3047374 upstream.

Commit a096ccca6e initializes the "sk_uid" field in the protocol socket
(struct sock) from the "/dev/net/tun" device node's owner UID. Per
original commit 86741ec254 ("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 86741ec254 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 a096ccca6e
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: a096ccca6e ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Laszlo Ersek 2023-07-31 18:42:36 +02:00 committed by Greg Kroah-Hartman
parent adacc3a954
commit 4ed3eed99e
1 changed files with 1 additions and 1 deletions
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2
drivers/net/tun.c
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@ -3411,7 +3411,7 @@ 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;