Vulnerability CVE-2024-38596
Published: 2024-06-19

Description:
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

 References:
https://git.kernel.org/stable/c/fca6072e1a7b1e709ada5604b951513b89b4bd0a
https://git.kernel.org/stable/c/de6641d213373fbde9bbdd7c4b552254bc9f82fe
https://git.kernel.org/stable/c/4d51845d734a4c5d079e56e0916f936a55e15055
https://git.kernel.org/stable/c/9aa8773abfa0e954136875b4cbf2df4cf638e8a5
https://git.kernel.org/stable/c/8299e4d778f664b31b67cf4cf3d5409de2ecb92c
https://git.kernel.org/stable/c/0688d4e499bee3f2749bca27329bd128686230cb
https://git.kernel.org/stable/c/a4c88072abcaca593cefe70f90e9d3707526e8f9
https://git.kernel.org/stable/c/a52fa2addfcccc2c5a0217fd45562605088c018b
https://git.kernel.org/stable/c/540bf24fba16b88c1b3b9353927204b4f1074e25
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