CVE-2024-35970
Linux Kernel af_unix: Stale OOB skb Handling Vulnerability
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 >>> c2.recv(5) # OOB data is not received b'hell' >>> c2.recv(5) # OOB date is skipped b'world' >>> c2.recv(5, MSG_OOB) # This should return an error b'o' In the same situation, TCP actually returns -EINVAL for the last recv(). Also, if we do not clear unix_sk(sk)->oob_skb, unix_poll() always set EPOLLPRI even though the data has passed through by previous recv(). To avoid these issues, we must clear unix_sk(sk)->oob_skb when dequeuing it from recv queue. The reason why the old GC did not trigger the deadlock is because the old GC relied on the receive queue to detect the loop. When it is triggered, the socket with OOB data is marked as GC candidate because file refcount == inflight count (1). However, after traversing all inflight sockets, the socket still has a positive inflight count (1), thus the socket is excluded from candidates. Then, the old GC lose the chance to garbage-collect the socket. With the old GC, the repro continues to create true garbage that will never be freed nor detected by kmemleak as it's linked to the global inflight list. That's why we couldn't even notice the issue.
INFO
Published Date :
May 20, 2024, 10:15 a.m.
Last Modified :
May 20, 2024, 1 p.m.
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Remotely Exploitable :
No
Impact Score :
Exploitability Score :
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CVE-2024-35970
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Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
May. 29, 2024
Action Type Old Value New Value -
CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
May. 20, 2024
Action Type Old Value New Value Added 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 >>> c2.recv(5) # OOB data is not received b'hell' >>> c2.recv(5) # OOB date is skipped b'world' >>> c2.recv(5, MSG_OOB) # This should return an error b'o' In the same situation, TCP actually returns -EINVAL for the last recv(). Also, if we do not clear unix_sk(sk)->oob_skb, unix_poll() always set EPOLLPRI even though the data has passed through by previous recv(). To avoid these issues, we must clear unix_sk(sk)->oob_skb when dequeuing it from recv queue. The reason why the old GC did not trigger the deadlock is because the old GC relied on the receive queue to detect the loop. When it is triggered, the socket with OOB data is marked as GC candidate because file refcount == inflight count (1). However, after traversing all inflight sockets, the socket still has a positive inflight count (1), thus the socket is excluded from candidates. Then, the old GC lose the chance to garbage-collect the socket. With the old GC, the repro continues to create true garbage that will never be freed nor detected by kmemleak as it's linked to the global inflight list. That's why we couldn't even notice the issue. Added Reference kernel.org https://git.kernel.org/stable/c/b4bc99d04c689b5652665394ae8d3e02fb754153 [No types assigned] Added Reference kernel.org https://git.kernel.org/stable/c/84a352b7eba1142a95441380058985ff19f25ec9 [No types assigned] Added Reference kernel.org https://git.kernel.org/stable/c/601a89ea24d05089debfa2dc896ea9f5937ac7a6 [No types assigned] Added Reference kernel.org https://git.kernel.org/stable/c/698a95ade1a00e6494482046902b986dfffd1caf [No types assigned] Added Reference kernel.org https://git.kernel.org/stable/c/b46f4eaa4f0ec38909fb0072eea3aeddb32f954e [No types assigned]
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2024-35970
is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2024-35970
weaknesses.