CVE-2023-53685

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 run concurrently. Otherwise, there would be a small race window: write() ioctl(IFF_DETACH_QUEUE) `- tun_get_user `- __tun_detach |- if (tfile->detached) |- tun_disable_queue | `-> false | `- tfile->detached = tun | `- tun_queue_purge |- spin_lock_bh(&queue->lock) `- __skb_queue_tail(queue, skb) Another solution is to call tun_queue_purge() when closing and reattaching the detached queue, but it could paper over another problems. Also, we do the same kind of test for IFF_NAPI_FRAGS. [0]: unreferenced object 0xffff88801edbc800 (size 2048): comm "syz-executor.1", pid 33269, jiffies 4295743834 (age 18.756s) hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 07 40 00 00 00 00 00 00 00 00 00 00 00 00 ...@............ backtrace: [ ] __do_kmalloc_node mm/slab_common.c:965 [inline] [ ] __kmalloc+0x4a/0x130 mm/slab_common.c:979 [ ] kmalloc include/linux/slab.h:563 [inline] [ ] sk_prot_alloc+0xef/0x1b0 net/core/sock.c:2035 [ ] sk_alloc+0x36/0x2f0 net/core/sock.c:2088 [ ] tun_chr_open+0x3d/0x190 drivers/net/tun.c:3438 [ ] misc_open+0x1a6/0x1f0 drivers/char/misc.c:165 [ ] chrdev_open+0x111/0x300 fs/char_dev.c:414 [ ] do_dentry_open+0x2f9/0x750 fs/open.c:920 [ ] do_open fs/namei.c:3636 [inline] [ ] path_openat+0x143f/0x1a30 fs/namei.c:3791 [ ] do_filp_open+0xce/0x1c0 fs/namei.c:3818 [ ] do_sys_openat2+0xf0/0x260 fs/open.c:1356 [ ] do_sys_open fs/open.c:1372 [inline] [ ] __do_sys_openat fs/open.c:1388 [inline] [ ] __se_sys_openat fs/open.c:1383 [inline] [ ] __x64_sys_openat+0x83/0xf0 fs/open.c:1383 [ ] do_syscall_x64 arch/x86/entry/common.c:50 [inline] [ ] do_syscall_64+0x3c/0x90 arch/x86/entry/common.c:80 [ ] entry_SYSCALL_64_after_hwframe+0x72/0xdc unreferenced object 0xffff88802f671700 (size 240): comm "syz-executor.1", pid 33269, jiffies 4295743854 (age 18.736s) hex dump (first 32 bytes): 68 c9 db 1e 80 88 ff ff 68 c9 db 1e 80 88 ff ff h.......h....... 00 c0 7b 2f 80 88 ff ff 00 c8 db 1e 80 88 ff ff ..{/............ backtrace: [ ] __alloc_skb+0x223/0x250 net/core/skbuff.c:644 [ ] alloc_skb include/linux/skbuff.h:1288 [inline] [ ] alloc_skb_with_frags+0x6f/0x350 net/core/skbuff.c:6378 [ ] sock_alloc_send_pskb+0x3ac/0x3e0 net/core/sock.c:2729 [ ] tun_alloc_skb drivers/net/tun.c:1529 [inline] [< ---truncated---