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

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commit 9bc3047374d5bec163e83e743709e23753376f0c upstream.

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 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 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".

Bug: 295995961
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit b6846d7c40)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I2540ac5876ca7dad39e1b867a5e09a5c9c69bb86
This commit is contained in:
Laszlo Ersek 2023-07-31 18:42:36 +02:00 committed by Treehugger Robot
parent 0adc759b0c
commit ec1f17ddac
1 changed files with 1 additions and 1 deletions
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2
drivers/net/tun.c
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@ -3449,7 +3449,7 @@ 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;