CVE-2024-38596

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