af_unix: Fix data races in unix_release_sock/unix_stream_sendmsg

Vulnerability 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