CVE-2023-53489
Publication date:
01/10/2025
In the Linux kernel, the following vulnerability has been resolved:<br />
<br />
tcp/udp: Fix memleaks of sk and zerocopy skbs with TX timestamp.<br />
<br />
syzkaller reported [0] memory leaks of an UDP socket and ZEROCOPY<br />
skbs. We can reproduce the problem with these sequences:<br />
<br />
sk = socket(AF_INET, SOCK_DGRAM, 0)<br />
sk.setsockopt(SOL_SOCKET, SO_TIMESTAMPING, SOF_TIMESTAMPING_TX_SOFTWARE)<br />
sk.setsockopt(SOL_SOCKET, SO_ZEROCOPY, 1)<br />
sk.sendto(b&#39;&#39;, MSG_ZEROCOPY, (&#39;127.0.0.1&#39;, 53))<br />
sk.close()<br />
<br />
sendmsg() calls msg_zerocopy_alloc(), which allocates a skb, sets<br />
skb->cb->ubuf.refcnt to 1, and calls sock_hold(). Here, struct<br />
ubuf_info_msgzc indirectly holds a refcnt of the socket. When the<br />
skb is sent, __skb_tstamp_tx() clones it and puts the clone into<br />
the socket&#39;s error queue with the TX timestamp.<br />
<br />
When the original skb is received locally, skb_copy_ubufs() calls<br />
skb_unclone(), and pskb_expand_head() increments skb->cb->ubuf.refcnt.<br />
This additional count is decremented while freeing the skb, but struct<br />
ubuf_info_msgzc still has a refcnt, so __msg_zerocopy_callback() is<br />
not called.<br />
<br />
The last refcnt is not released unless we retrieve the TX timestamped<br />
skb by recvmsg(). Since we clear the error queue in inet_sock_destruct()<br />
after the socket&#39;s refcnt reaches 0, there is a circular dependency.<br />
If we close() the socket holding such skbs, we never call sock_put()<br />
and leak the count, sk, and skb.<br />
<br />
TCP has the same problem, and commit e0c8bccd40fc ("net: stream:<br />
purge sk_error_queue in sk_stream_kill_queues()") tried to fix it<br />
by calling skb_queue_purge() during close(). However, there is a<br />
small chance that skb queued in a qdisc or device could be put<br />
into the error queue after the skb_queue_purge() call.<br />
<br />
In __skb_tstamp_tx(), the cloned skb should not have a reference<br />
to the ubuf to remove the circular dependency, but skb_clone() does<br />
not call skb_copy_ubufs() for zerocopy skb. So, we need to call<br />
skb_orphan_frags_rx() for the cloned skb to call skb_copy_ubufs().<br />
<br />
[0]:<br />
BUG: memory leak<br />
unreferenced object 0xffff88800c6d2d00 (size 1152):<br />
comm "syz-executor392", pid 264, jiffies 4294785440 (age 13.044s)<br />
hex dump (first 32 bytes):<br />
00 00 00 00 00 00 00 00 cd af e8 81 00 00 00 00 ................<br />
02 00 07 40 00 00 00 00 00 00 00 00 00 00 00 00 ...@............<br />
backtrace:<br />
[] sk_prot_alloc+0x64/0x2a0 net/core/sock.c:2024<br />
[] sk_alloc+0x3b/0x800 net/core/sock.c:2083<br />
[] inet_create net/ipv4/af_inet.c:319 [inline]<br />
[] inet_create+0x31e/0xe40 net/ipv4/af_inet.c:245<br />
[] __sock_create+0x2ab/0x550 net/socket.c:1515<br />
[] sock_create net/socket.c:1566 [inline]<br />
[] __sys_socket_create net/socket.c:1603 [inline]<br />
[] __sys_socket_create net/socket.c:1588 [inline]<br />
[] __sys_socket+0x138/0x250 net/socket.c:1636<br />
[] __do_sys_socket net/socket.c:1649 [inline]<br />
[] __se_sys_socket net/socket.c:1647 [inline]<br />
[] __x64_sys_socket+0x73/0xb0 net/socket.c:1647<br />
[] do_syscall_x64 arch/x86/entry/common.c:50 [inline]<br />
[] do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80<br />
[] entry_SYSCALL_64_after_hwframe+0x63/0xcd<br />
<br />
BUG: memory leak<br />
unreferenced object 0xffff888017633a00 (size 240):<br />
comm "syz-executor392", pid 264, jiffies 4294785440 (age 13.044s)<br />
hex dump (first 32 bytes):<br />
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................<br />
00 00 00 00 00 00 00 00 00 2d 6d 0c 80 88 ff ff .........-m.....<br />
backtrace:<br />
[] __alloc_skb+0x229/0x320 net/core/skbuff.c:497<br />
[] alloc_skb include/linux/skbuff.h:1265 [inline]<br />
[] sock_omalloc+0xaa/0x190 net/core/sock.c:2596<br />
[] msg_zerocopy_alloc net/core/skbuff.c:1294 [inline]<br />
[]<br />
---truncated---
Severity CVSS v4.0: Pending analysis
Last modification:
02/10/2025