net: tap_open(): set sk_uid from current_fsuid()
commit 5c9241f3ceab3257abe2923a59950db0dc8bb737 upstream.
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".
BUG=b/296028775
TEST=presubmit
SOURCE=UPSTREAM(5c9241f3ceab)
RELEASE_NOTE=Fixed CVE-2023-4194 in the Linux kernel.
cos-patch: security-moderate
Fixes: 66b2c338adce ("tap: tap_open(): correctly initialize socket uid")
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2173435
Change-Id: Ib00b3f3a33be8a839e4157bd0c051f0007f93e35
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>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/55116
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Main-Branch-Verified: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Oleksandr Tymoshenko <ovt@google.com>
diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 3c468ef..8c01085 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -533,7 +533,7 @@
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;