CVE-2023-53685

Technical Description

In the Linux kernel, the following vulnerability has been resolved:

tun: Fix memory leak for detached NAPI queue.

syzkaller reported [0] memory leaks of sk and skb related to the TUN

device with no repro, but we can reproduce it easily with:

struct ifreq ifr = {}

int fd_tun, fd_tmp;

char buf[4] = {};

fd_tun = openat(AT_FDCWD, "/dev/net/tun", O_WRONLY, 0);

ifr.ifr_flags = IFF_TUN | IFF_NAPI | IFF_MULTI_QUEUE;

ioctl(fd_tun, TUNSETIFF, &ifr);

ifr.ifr_flags = IFF_DETACH_QUEUE;

ioctl(fd_tun, TUNSETQUEUE, &ifr);

fd_tmp = socket(AF_PACKET, SOCK_PACKET, 0);

ifr.ifr_flags = IFF_UP;

ioctl(fd_tmp, SIOCSIFFLAGS, &ifr);

write(fd_tun, buf, sizeof(buf));

close(fd_tun);

If we enable NAPI and multi-queue on a TUN device, we can put skb into

tfile->sk.sk_write_queue after the queue is detached. We should prevent

it by checking tfile->detached before queuing skb.

Note this must be done under tfile->sk.sk_write_queue.lock because write()

and ioctl(IFF_DETACH_QUEUE) can

Remediation

Check the references section for vendor advisories and patches from linux. Update linux_kernel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected Products

References