netdev - Re: [PATCH net v4] netlabel: fix RCU annotation for IPv4 options on socket creation

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Date: Thu, 9 May 2024 15:13:36 -0400
From: Paul Moore <paul@...l-moore.com>
To: Davide Caratti <dcaratti@...hat.com>
Cc: netdev@...r.kernel.org, casey@...aufler-ca.com, davem@...emloft.net, 
	edumazet@...gle.com, kuba@...nel.org, linux-security-module@...r.kernel.org, 
	pabeni@...hat.com, xmu@...hat.com
Subject: Re: [PATCH net v4] netlabel: fix RCU annotation for IPv4 options on
 socket creation

On Thu, May 9, 2024 at 6:36 AM Davide Caratti <dcaratti@...hat.com> wrote:
>
> Xiumei reports the following splat when netlabel and TCP socket are used:
>
>  =============================
>  WARNING: suspicious RCU usage
>  6.9.0-rc2+ #637 Not tainted
>  -----------------------------
>  net/ipv4/cipso_ipv4.c:1880 suspicious rcu_dereference_protected() usage!
>
>  other info that might help us debug this:
>
>  rcu_scheduler_active = 2, debug_locks = 1
>  1 lock held by ncat/23333:
>   #0: ffffffff906030c0 (rcu_read_lock){....}-{1:2}, at: netlbl_sock_setattr+0x25/0x1b0
>
>  stack backtrace:
>  CPU: 11 PID: 23333 Comm: ncat Kdump: loaded Not tainted 6.9.0-rc2+ #637
>  Hardware name: Supermicro SYS-6027R-72RF/X9DRH-7TF/7F/iTF/iF, BIOS 3.0  07/26/2013
>  Call Trace:
>   <TASK>
>   dump_stack_lvl+0xa9/0xc0
>   lockdep_rcu_suspicious+0x117/0x190
>   cipso_v4_sock_setattr+0x1ab/0x1b0
>   netlbl_sock_setattr+0x13e/0x1b0
>   selinux_netlbl_socket_post_create+0x3f/0x80
>   selinux_socket_post_create+0x1a0/0x460
>   security_socket_post_create+0x42/0x60
>   __sock_create+0x342/0x3a0
>   __sys_socket_create.part.22+0x42/0x70
>   __sys_socket+0x37/0xb0
>   __x64_sys_socket+0x16/0x20
>   do_syscall_64+0x96/0x180
>   ? do_user_addr_fault+0x68d/0xa30
>   ? exc_page_fault+0x171/0x280
>   ? asm_exc_page_fault+0x22/0x30
>   entry_SYSCALL_64_after_hwframe+0x71/0x79
>  RIP: 0033:0x7fbc0ca3fc1b
>  Code: 73 01 c3 48 8b 0d 05 f2 1b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 29 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d d5 f1 1b 00 f7 d8 64 89 01 48
>  RSP: 002b:00007fff18635208 EFLAGS: 00000246 ORIG_RAX: 0000000000000029
>  RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007fbc0ca3fc1b
>  RDX: 0000000000000006 RSI: 0000000000000001 RDI: 0000000000000002
>  RBP: 000055d24f80f8a0 R08: 0000000000000003 R09: 0000000000000001
>
> R10: 0000000000020000 R11: 0000000000000246 R12: 000055d24f80f8a0
>  R13: 0000000000000000 R14: 000055d24f80fb88 R15: 0000000000000000
>   </TASK>
>
> The current implementation of cipso_v4_sock_setattr() replaces IP options
> under the assumption that the caller holds the socket lock; however, such
> assumption is not true, nor needed, in selinux_socket_post_create() hook.
>
> Let all callers of cipso_v4_sock_setattr() specify the "socket lock held"
> condition, except selinux_socket_post_create() _ where such condition can
> safely be set as true even without holding the socket lock.
>
> v4:
>  - fix build when CONFIG_LOCKDEP is unset (thanks kernel test robot)
>
> v3:
>  - rename variable to 'sk_locked' (thanks Paul Moore)
>  - keep rcu_replace_pointer() open-coded and re-add NULL check of 'old',
>    these two changes will be posted in another patch (thanks Paul Moore)
>
> v2:
>  - pass lockdep_sock_is_held() through a boolean variable in the stack
>    (thanks Eric Dumazet, Paul Moore, Casey Schaufler)
>  - use rcu_replace_pointer() instead of rcu_dereference_protected() +
>    rcu_assign_pointer()
>  - remove NULL check of 'old' before kfree_rcu()
>
> Fixes: f6d8bd051c39 ("inet: add RCU protection to inet->opt")
> Reported-by: Xiumei Mu <xmu@...hat.com>
> Acked-by: Paul Moore <paul@...l-moore.com>
> Signed-off-by: Davide Caratti <dcaratti@...hat.com>
> ---
>  include/net/cipso_ipv4.h     |  6 ++++--
>  include/net/netlabel.h       | 12 ++++++++++--
>  net/ipv4/cipso_ipv4.c        |  7 ++++---
>  net/netlabel/netlabel_kapi.c | 26 +++++++++++++++++++++++---
>  security/selinux/netlabel.c  |  5 ++++-
>  security/smack/smack_lsm.c   |  3 ++-
>  6 files changed, 47 insertions(+), 12 deletions(-)

...

> +/**
> + * netlbl_sk_lock_check - Check if the socket lock has been acquired.
> + * @sk: the socket to check
> + *
> + * Description: check if @sk is locked. Returns true if socket @sk is locked
> + * or if lock debugging is disabled at runtime or compile-time
> + *
> + */
> +bool netlbl_sk_lock_check(struct sock *sk)
> +{
> +#ifdef CONFIG_LOCKDEP
> +       if (debug_locks)
> +               return lockdep_sock_is_held(sk);
> +#endif
> +       return true;
> +}

It might be cleaner to do this:

#ifdef CONFIG_LOCKDEP
bool netlbl_sk_lock_check(sk)
{
  if (debug_locks)
    return lockdep_sock_is_held(sk);
  return true;
}
#else
bool netlbl_sk_lock_check(sk)
{
  return true;
}
#endif

-- 
paul-moore.com