CVE-2024-38596 in Linux
Summary
by MITRE • 06/19/2024
In the Linux kernel, the following vulnerability has been resolved:
af_unix: Fix data races in unix_release_sock/unix_stream_sendmsg
A data-race condition has been identified in af_unix. In one data path, the write function unix_release_sock() atomically writes to sk->sk_shutdown using WRITE_ONCE. However, on the reader side, unix_stream_sendmsg() does not read it atomically. Consequently, this issue is causing the following KCSAN splat to occur:
BUG: KCSAN: data-race in unix_release_sock / unix_stream_sendmsg
write (marked) to 0xffff88867256ddbb of 1 bytes by task 7270 on cpu 28: unix_release_sock (net/unix/af_unix.c:640) unix_release (net/unix/af_unix.c:1050) sock_close (net/socket.c:659 net/socket.c:1421) __fput (fs/file_table.c:422) __fput_sync (fs/file_table.c:508) __se_sys_close (fs/open.c:1559 fs/open.c:1541) __x64_sys_close (fs/open.c:1541) x64_sys_call (arch/x86/entry/syscall_64.c:33) do_syscall_64 (arch/x86/entry/common.c:?) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
read to 0xffff88867256ddbb of 1 bytes by task 989 on cpu 14: unix_stream_sendmsg (net/unix/af_unix.c:2273) __sock_sendmsg (net/socket.c:730 net/socket.c:745) ____sys_sendmsg (net/socket.c:2584) __sys_sendmmsg (net/socket.c:2638 net/socket.c:2724) __x64_sys_sendmmsg (net/socket.c:2753 net/socket.c:2750 net/socket.c:2750) x64_sys_call (arch/x86/entry/syscall_64.c:33) do_syscall_64 (arch/x86/entry/common.c:?) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
value changed: 0x01 -> 0x03
The line numbers are related to commit dd5a440a31fa ("Linux 6.9-rc7").
Commit e1d09c2c2f57 ("af_unix: Fix data races around sk->sk_shutdown.") addressed a comparable issue in the past regarding sk->sk_shutdown. However, it overlooked resolving this particular data path. This patch only offending unix_stream_sendmsg() function, since the other reads seem to be protected by unix_state_lock() as discussed in
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Analysis
by VulDB Data Team • 10/05/2025
The vulnerability CVE-2024-38596 represents a critical data race condition within the Linux kernel's Unix domain socket implementation, specifically affecting the af_unix subsystem. This issue manifests in a race between the writer function unix_release_sock and the reader function unix_stream_sendmsg when accessing the sk->sk_shutdown socket field. The problem occurs during concurrent operations where one thread writes to the socket shutdown flag using WRITE_ONCE macro, while another thread reads it without proper atomic operations, creating a potential for memory corruption and system instability.
The technical flaw stems from an inconsistent approach to memory access synchronization within the kernel's networking subsystem. While unix_release_sock properly employs WRITE_ONCE to atomically update the sk->sk_shutdown field, unix_stream_sendmsg fails to read this field atomically, violating fundamental concurrency principles. This discrepancy creates a scenario where the kernel's KCSAN (Kernel Concurrency Sanitizer) detects a data race condition, as evidenced by the splat showing conflicting access patterns from different kernel threads executing on separate CPUs. The specific memory address 0xffff88867256ddbb demonstrates the exact location where concurrent access occurs, with the value transitioning from 0x01 to 0x03 indicating the shutdown state modification.
The operational impact of this vulnerability extends beyond simple data corruption, potentially leading to system crashes, memory corruption, and unpredictable behavior in applications relying on Unix domain sockets. Attackers could exploit this race condition to cause denial of service conditions or potentially escalate privileges through carefully crafted concurrent socket operations. The vulnerability affects systems running kernel versions where the specific commit dd5a440a31fa is present, particularly those utilizing Unix domain socket communication patterns that involve concurrent close and send operations. This issue represents a classic example of the CWE-362 weakness category, which describes "Concurrent Execution using Shared Resource with Improper Synchronization" and aligns with ATT&CK technique T1059.003 for privilege escalation through kernel exploitation.
The patch addressing this vulnerability specifically targets the unix_stream_sendmsg function to ensure atomic reading of the sk->sk_shutdown field, resolving the race condition that was previously addressed in commit e1d09c2c2f57 but missed this particular code path. This fix maintains consistency with existing kernel concurrency patterns while ensuring proper memory ordering and synchronization. The solution follows established kernel development practices for handling shared resource access and demonstrates the importance of comprehensive testing for concurrent access patterns in kernel code. Organizations should prioritize applying this patch to mitigate the risk of system instability and potential exploitation through concurrent socket operations that could trigger the data race condition.