CVE-2023-4194: Kernel: tap: tap_open(): correctly initialize socket uid next fix of i_uid to current_fsuid

A flaw found in the Linux Kernel. The tun/tap sockets have their socket UID hardcoded to 0 due to a type confusion in their initialization function. While it will be often correct, as tuntap devices require CAPNETADMIN, it may not always be the case, e.g., a non-root user only having that capability. This would make tun/tap sockets being incorrectly treated in filtering/routing decisions, possibly bypassing network filters. The original fix for the CVE-2023-1076 was incorrect. The problem is that the following upstream commits (that were fix for the CVE-2023-1076) - a096ccca6e50 ("tun: tunchropen(): correctly initialize socket uid"), - 66b2c338adce ("tap: tapopen(): correctly initialize socket uid"), pass "inode->iuid" to sockinitdatauid() as the last parameter and that turns out to be entirely bogus.

References: https://lore.kernel.org/all/20230731164237.48365-1-lersek@redhat.com/ https://lore.kernel.org/all/20230731164237.48365-2-lersek@redhat.com/ https://lore.kernel.org/all/20230731164237.48365-3-lersek@redhat.com/