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Message-ID: <2025100710-CVE-2023-53685-68d1@gregkh>
Date: Tue, 7 Oct 2025 17:21:44 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2023-53685: tun: Fix memory leak for detached NAPI queue.
From: Greg Kroah-Hartman <gregkh@...nel.org>
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 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:
[<000000008c16ea3d>] __do_kmalloc_node mm/slab_common.c:965 [inline]
[<000000008c16ea3d>] __kmalloc+0x4a/0x130 mm/slab_common.c:979
[<000000003addde56>] kmalloc include/linux/slab.h:563 [inline]
[<000000003addde56>] sk_prot_alloc+0xef/0x1b0 net/core/sock.c:2035
[<000000003e20621f>] sk_alloc+0x36/0x2f0 net/core/sock.c:2088
[<0000000028e43843>] tun_chr_open+0x3d/0x190 drivers/net/tun.c:3438
[<000000001b0f1f28>] misc_open+0x1a6/0x1f0 drivers/char/misc.c:165
[<000000004376f706>] chrdev_open+0x111/0x300 fs/char_dev.c:414
[<00000000614d379f>] do_dentry_open+0x2f9/0x750 fs/open.c:920
[<000000008eb24774>] do_open fs/namei.c:3636 [inline]
[<000000008eb24774>] path_openat+0x143f/0x1a30 fs/namei.c:3791
[<00000000955077b5>] do_filp_open+0xce/0x1c0 fs/namei.c:3818
[<00000000b78973b0>] do_sys_openat2+0xf0/0x260 fs/open.c:1356
[<00000000057be699>] do_sys_open fs/open.c:1372 [inline]
[<00000000057be699>] __do_sys_openat fs/open.c:1388 [inline]
[<00000000057be699>] __se_sys_openat fs/open.c:1383 [inline]
[<00000000057be699>] __x64_sys_openat+0x83/0xf0 fs/open.c:1383
[<00000000a7d2182d>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
[<00000000a7d2182d>] do_syscall_64+0x3c/0x90 arch/x86/entry/common.c:80
[<000000004cc4e8c4>] 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:
[<00000000e9d9fdb6>] __alloc_skb+0x223/0x250 net/core/skbuff.c:644
[<000000002c3e4e0b>] alloc_skb include/linux/skbuff.h:1288 [inline]
[<000000002c3e4e0b>] alloc_skb_with_frags+0x6f/0x350 net/core/skbuff.c:6378
[<00000000825f98d7>] sock_alloc_send_pskb+0x3ac/0x3e0 net/core/sock.c:2729
[<00000000e9eb3df3>] tun_alloc_skb drivers/net/tun.c:1529 [inline]
[<00000000e9eb3df3>] tun_get_user+0x5e1/0x1f90 drivers/net/tun.c:1841
[<0000000053096912>] tun_chr_write_iter+0xac/0x120 drivers/net/tun.c:2035
[<00000000b9282ae0>] call_write_iter include/linux/fs.h:1868 [inline]
[<00000000b9282ae0>] new_sync_write fs/read_write.c:491 [inline]
[<00000000b9282ae0>] vfs_write+0x40f/0x530 fs/read_write.c:584
[<00000000524566e4>] ksys_write+0xa1/0x170 fs/read_write.c:637
[<00000000a7d2182d>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
[<00000000a7d2182d>] do_syscall_64+0x3c/0x90 arch/x86/entry/common.c:80
[<000000004cc4e8c4>] entry_SYSCALL_64_after_hwframe+0x72/0xdc
The Linux kernel CVE team has assigned CVE-2023-53685 to this issue.
Affected and fixed versions
===========================
Issue introduced in 3.8 with commit cde8b15f1aabe327038ee4e0e11dd6b798572f69 and fixed in 6.1.30 with commit 9cae243b9ae25adfe468cd47ceca591f6725b79c
Issue introduced in 3.8 with commit cde8b15f1aabe327038ee4e0e11dd6b798572f69 and fixed in 6.3.4 with commit 0d20210a190f76db9ec35ee4e0fc77e6c7a148f5
Issue introduced in 3.8 with commit cde8b15f1aabe327038ee4e0e11dd6b798572f69 and fixed in 6.4 with commit 82b2bc279467c875ec36f8ef820f00997c2a4e8e
Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.
Unaffected versions might change over time as fixes are backported to
older supported kernel versions. The official CVE entry at
https://cve.org/CVERecord/?id=CVE-2023-53685
will be updated if fixes are backported, please check that for the most
up to date information about this issue.
Affected files
==============
The file(s) affected by this issue are:
drivers/net/tun.c
Mitigation
==========
The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes. Individual
changes are never tested alone, but rather are part of a larger kernel
release. Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all. If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
https://git.kernel.org/stable/c/9cae243b9ae25adfe468cd47ceca591f6725b79c
https://git.kernel.org/stable/c/0d20210a190f76db9ec35ee4e0fc77e6c7a148f5
https://git.kernel.org/stable/c/82b2bc279467c875ec36f8ef820f00997c2a4e8e
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