netdev - Re: [PATCH v1 net] af_unix: Annotate data-races around sk->sk

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Tue, 21 May 2024 06:16:54 +0200
From: Dmitry Vyukov <dvyukov@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org, 
	syzkaller <syzkaller@...glegroups.com>
Subject: Re: [PATCH v1 net] af_unix: Annotate data-races around sk->sk_hash.

On Sat, 18 May 2024 at 03:14, 'Kuniyuki Iwashima' via syzkaller
<syzkaller@...glegroups.com> wrote:
>
> syzkaller reported data-race of sk->sk_hash in unix_autobind() [0],
> and the same ones exist in unix_bind_bsd() and unix_bind_abstract().
>
> The three bind() functions prefetch sk->sk_hash locklessly and
> use it later after validating that unix_sk(sk)->addr is NULL under
> unix_sk(sk)->bindlock.
>
> The prefetched sk->sk_hash is the hash value of unbound socket set
> in unix_create1() and does not change until bind() completes.
>
> There could be a chance that sk->sk_hash changes after the lockless
> read.  However, in such a case, non-NULL unix_sk(sk)->addr is visible
> under unix_sk(sk)->bindlock, and bind() returns -EINVAL without using
> the prefetched value.
>
> The KCSAN splat is false-positive, but let's use WRITE_ONCE() and
> READ_ONCE() to silence it.
>
> [0]:
> BUG: KCSAN: data-race in unix_autobind / unix_autobind
>
> write to 0xffff888034a9fb88 of 4 bytes by task 4468 on cpu 0:
>  __unix_set_addr_hash net/unix/af_unix.c:331 [inline]
>  unix_autobind+0x47a/0x7d0 net/unix/af_unix.c:1185
>  unix_dgram_connect+0x7e3/0x890 net/unix/af_unix.c:1373
>  __sys_connect_file+0xd7/0xe0 net/socket.c:2048
>  __sys_connect+0x114/0x140 net/socket.c:2065
>  __do_sys_connect net/socket.c:2075 [inline]
>  __se_sys_connect net/socket.c:2072 [inline]
>  __x64_sys_connect+0x40/0x50 net/socket.c:2072
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0x4f/0x110 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x46/0x4e
>
> read to 0xffff888034a9fb88 of 4 bytes by task 4465 on cpu 1:
>  unix_autobind+0x28/0x7d0 net/unix/af_unix.c:1134
>  unix_dgram_connect+0x7e3/0x890 net/unix/af_unix.c:1373
>  __sys_connect_file+0xd7/0xe0 net/socket.c:2048
>  __sys_connect+0x114/0x140 net/socket.c:2065
>  __do_sys_connect net/socket.c:2075 [inline]
>  __se_sys_connect net/socket.c:2072 [inline]
>  __x64_sys_connect+0x40/0x50 net/socket.c:2072
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0x4f/0x110 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x46/0x4e
>
> value changed: 0x000000e4 -> 0x000001e3
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 4465 Comm: syz-executor.0 Not tainted 6.8.0-12822-gcd51db110a7e #12
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
>
> Fixes: afd20b9290e1 ("af_unix: Replace the big lock with small locks.")
> Reported-by: syzkaller <syzkaller@...glegroups.com>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> ---
>  net/unix/af_unix.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 92a88ac070ca..e92b45e21664 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -327,8 +327,7 @@ static void __unix_set_addr_hash(struct net *net, struct sock *sk,
>  {
>         __unix_remove_socket(sk);
>         smp_store_release(&unix_sk(sk)->addr, addr);
> -
> -       sk->sk_hash = hash;
> +       WRITE_ONCE(sk->sk_hash, hash);
>         __unix_insert_socket(net, sk);
>  }
>
> @@ -1131,7 +1130,7 @@ static struct sock *unix_find_other(struct net *net,
>
>  static int unix_autobind(struct sock *sk)
>  {
> -       unsigned int new_hash, old_hash = sk->sk_hash;
> +       unsigned int new_hash, old_hash = READ_ONCE(sk->sk_hash);
>         struct unix_sock *u = unix_sk(sk);
>         struct net *net = sock_net(sk);
>         struct unix_address *addr;
> @@ -1195,7 +1194,7 @@ static int unix_bind_bsd(struct sock *sk, struct sockaddr_un *sunaddr,
>  {
>         umode_t mode = S_IFSOCK |
>                (SOCK_INODE(sk->sk_socket)->i_mode & ~current_umask());
> -       unsigned int new_hash, old_hash = sk->sk_hash;
> +       unsigned int new_hash, old_hash = READ_ONCE(sk->sk_hash);
>         struct unix_sock *u = unix_sk(sk);
>         struct net *net = sock_net(sk);
>         struct mnt_idmap *idmap;
> @@ -1261,7 +1260,7 @@ static int unix_bind_bsd(struct sock *sk, struct sockaddr_un *sunaddr,
>  static int unix_bind_abstract(struct sock *sk, struct sockaddr_un *sunaddr,
>                               int addr_len)
>  {
> -       unsigned int new_hash, old_hash = sk->sk_hash;
> +       unsigned int new_hash, old_hash = READ_ONCE(sk->sk_hash);
>         struct unix_sock *u = unix_sk(sk);
>         struct net *net = sock_net(sk);
>         struct unix_address *addr;



Hi,

I don't know much about this code, but perhaps these accesses must be
protected by bindlock instead?
It shouldn't autobind twice, right? Perhaps the code just tried to
save a line of code and moved the reads to the variable declaration
section.