cve/published/2025/CVE-2025-22058.mbox

From bippy-1.2.0 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@kernel.org>
To: <linux-cve-announce@vger.kernel.org>
Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org>
Subject: CVE-2025-22058: udp: Fix memory accounting leak.

Description
===========

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

udp: Fix memory accounting leak.

Matt Dowling reported a weird UDP memory usage issue.

Under normal operation, the UDP memory usage reported in /proc/net/sockstat
remains close to zero.  However, it occasionally spiked to 524,288 pages
and never dropped.  Moreover, the value doubled when the application was
terminated.  Finally, it caused intermittent packet drops.

We can reproduce the issue with the script below [0]:

  1. /proc/net/sockstat reports 0 pages

    # cat /proc/net/sockstat | grep UDP:
    UDP: inuse 1 mem 0

  2. Run the script till the report reaches 524,288

    # python3 test.py & sleep 5
    # cat /proc/net/sockstat | grep UDP:
    UDP: inuse 3 mem 524288  <-- (INT_MAX + 1) >> PAGE_SHIFT

  3. Kill the socket and confirm the number never drops

    # pkill python3 && sleep 5
    # cat /proc/net/sockstat | grep UDP:
    UDP: inuse 1 mem 524288

  4. (necessary since v6.0) Trigger proto_memory_pcpu_drain()

    # python3 test.py & sleep 1 && pkill python3

  5. The number doubles

    # cat /proc/net/sockstat | grep UDP:
    UDP: inuse 1 mem 1048577

The application set INT_MAX to SO_RCVBUF, which triggered an integer
overflow in udp_rmem_release().

When a socket is close()d, udp_destruct_common() purges its receive
queue and sums up skb->truesize in the queue.  This total is calculated
and stored in a local unsigned integer variable.

The total size is then passed to udp_rmem_release() to adjust memory
accounting.  However, because the function takes a signed integer
argument, the total size can wrap around, causing an overflow.

Then, the released amount is calculated as follows:

  1) Add size to sk->sk_forward_alloc.
  2) Round down sk->sk_forward_alloc to the nearest lower multiple of
      PAGE_SIZE and assign it to amount.
  3) Subtract amount from sk->sk_forward_alloc.
  4) Pass amount >> PAGE_SHIFT to __sk_mem_reduce_allocated().

When the issue occurred, the total in udp_destruct_common() was 2147484480
(INT_MAX + 833), which was cast to -2147482816 in udp_rmem_release().

At 1) sk->sk_forward_alloc is changed from 3264 to -2147479552, and
2) sets -2147479552 to amount.  3) reverts the wraparound, so we don't
see a warning in inet_sock_destruct().  However, udp_memory_allocated
ends up doubling at 4).

Since commit 3cd3399dd7a8 ("net: implement per-cpu reserves for
memory_allocated"), memory usage no longer doubles immediately after
a socket is close()d because __sk_mem_reduce_allocated() caches the
amount in udp_memory_per_cpu_fw_alloc.  However, the next time a UDP
socket receives a packet, the subtraction takes effect, causing UDP
memory usage to double.

This issue makes further memory allocation fail once the socket's
sk->sk_rmem_alloc exceeds net.ipv4.udp_rmem_min, resulting in packet
drops.

To prevent this issue, let's use unsigned int for the calculation and
call sk_forward_alloc_add() only once for the small delta.

Note that first_packet_length() also potentially has the same problem.

[0]:
from socket import *

SO_RCVBUFFORCE = 33
INT_MAX = (2 ** 31) - 1

s = socket(AF_INET, SOCK_DGRAM)
s.bind(('', 0))
s.setsockopt(SOL_SOCKET, SO_RCVBUFFORCE, INT_MAX)

c = socket(AF_INET, SOCK_DGRAM)
c.connect(s.getsockname())

data = b'a' * 100

while True:
    c.send(data)

The Linux kernel CVE team has assigned CVE-2025-22058 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.10 with commit f970bd9e3a06f06df8d8ecf1f8ad2c8615cc17eb and fixed in 6.1.134 with commit 9122fec396950cc866137af7154b1d0d989be52e
	Issue introduced in 4.10 with commit f970bd9e3a06f06df8d8ecf1f8ad2c8615cc17eb and fixed in 6.6.87 with commit aeef6456692c6f11ae53d278df64f1316a2a405a
	Issue introduced in 4.10 with commit f970bd9e3a06f06df8d8ecf1f8ad2c8615cc17eb and fixed in 6.12.23 with commit a116b271bf3cb72c8155b6b7f39083c1b80dcd00
	Issue introduced in 4.10 with commit f970bd9e3a06f06df8d8ecf1f8ad2c8615cc17eb and fixed in 6.13.11 with commit c4bac6c398118fba79e32b1cd01db22dbfe29fbf
	Issue introduced in 4.10 with commit f970bd9e3a06f06df8d8ecf1f8ad2c8615cc17eb and fixed in 6.14.2 with commit 3836029448e76c1e6f77cc5fe0adc09b018b5fa8
	Issue introduced in 4.10 with commit f970bd9e3a06f06df8d8ecf1f8ad2c8615cc17eb and fixed in 6.15 with commit df207de9d9e7a4d92f8567e2c539d9c8c12fd99d

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-2025-22058
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:
	net/ipv4/udp.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/9122fec396950cc866137af7154b1d0d989be52e
	https://git.kernel.org/stable/c/aeef6456692c6f11ae53d278df64f1316a2a405a
	https://git.kernel.org/stable/c/a116b271bf3cb72c8155b6b7f39083c1b80dcd00
	https://git.kernel.org/stable/c/c4bac6c398118fba79e32b1cd01db22dbfe29fbf
	https://git.kernel.org/stable/c/3836029448e76c1e6f77cc5fe0adc09b018b5fa8
	https://git.kernel.org/stable/c/df207de9d9e7a4d92f8567e2c539d9c8c12fd99d