Description

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

af_unix: Clear stale u->oob_skb.

syzkaller started to report deadlock of unix_gc_lock after commit
4090fa373f0e ("af_unix: Replace garbage collection algorithm."), but
it just uncovers the bug that has been there since commit 314001f0bf92
("af_unix: Add OOB support").

The repro basically does the following.

from socket import *
from array import array

c1, c2 = socketpair(AF_UNIX, SOCK_STREAM)
c1.sendmsg([b'a'], [(SOL_SOCKET, SCM_RIGHTS, array("i", [c2.fileno()]))], MSG_OOB)
c2.recv(1) # blocked as no normal data in recv queue

c2.close() # done async and unblock recv()
c1.close() # done async and trigger GC

A socket sends its file descriptor to itself as OOB data and tries to
receive normal data, but finally recv() fails due to async close().

The problem here is wrong handling of OOB skb in manage_oob(). When
recvmsg() is called without MSG_OOB, manage_oob() is called to check
if the peeked skb is OOB skb. In such a case, manage_oob() pops it
out of the receive queue but does not clear unix_sock(sk)->oob_skb.
This is wrong in terms of uAPI.

Let's say we send "hello" with MSG_OOB, and "world" without MSG_OOB.
The 'o' is handled as OOB data. When recv() is called twice without
MSG_OOB, the OOB data should be lost.

>>> from socket import *
>>> c1, c2 = socketpair(AF_UNIX, SOCK_STREAM, 0)
>>> c1.send(b'hello', MSG_OOB) # 'o' is OOB data
5
>>> c1.send(b'world')
5
>>> ...

Classification

CVE ID: CVE-2024-35970

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.05% (probability of being exploited)

EPSS Percentile: 17.83% (scored less or equal to compared to others)

EPSS Date: 2025-02-04 (when was this score calculated)

References

https://git.kernel.org/stable/c/b4bc99d04c689b5652665394ae8d3e02fb754153
https://git.kernel.org/stable/c/84a352b7eba1142a95441380058985ff19f25ec9
https://git.kernel.org/stable/c/601a89ea24d05089debfa2dc896ea9f5937ac7a6
https://git.kernel.org/stable/c/698a95ade1a00e6494482046902b986dfffd1caf
https://git.kernel.org/stable/c/b46f4eaa4f0ec38909fb0072eea3aeddb32f954e

Timeline