linux-kernel - Re: [PATCH RFC] pid: make setpgid() system call use RCU read-side critical section

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]

Message-ID: <4C7C0BAB.3000709@suse.cz>
Date:	Mon, 30 Aug 2010 21:51:07 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	paulmck@...ux.vnet.ibm.com
CC:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, jmorris@...ei.org,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH RFC] pid: make setpgid() system call use RCU read-side
 critical section

Ccing Oleg.

On 08/30/2010 07:26 PM, Paul E. McKenney wrote:
> [   23.584720] ===================================================
> [   23.585059] [ INFO: suspicious rcu_dereference_check() usage. ]
> [   23.585176] ---------------------------------------------------
> [   23.585176] kernel/pid.c:419 invoked rcu_dereference_check() without protection!
> [   23.585176]
> [   23.585176] other info that might help us debug this:
> [   23.585176]
> [   23.585176]
> [   23.585176] rcu_scheduler_active = 1, debug_locks = 1
> [   23.585176] 1 lock held by rc.sysinit/728:
> [   23.585176]  #0:  (tasklist_lock){.+.+..}, at: [<ffffffff8104771f>] sys_setpgid+0x5f/0x193
> [   23.585176]
> [   23.585176] stack backtrace:
> [   23.585176] Pid: 728, comm: rc.sysinit Not tainted 2.6.36-rc2 #2
> [   23.585176] Call Trace:
> [   23.585176]  [<ffffffff8105b436>] lockdep_rcu_dereference+0x99/0xa2
> [   23.585176]  [<ffffffff8104c324>] find_task_by_pid_ns+0x50/0x6a
> [   23.585176]  [<ffffffff8104c35b>] find_task_by_vpid+0x1d/0x1f
> [   23.585176]  [<ffffffff81047727>] sys_setpgid+0x67/0x193
> [   23.585176]  [<ffffffff810029eb>] system_call_fastpath+0x16/0x1b
> [   24.959669] type=1400 audit(1282938522.956:4): avc:  denied  { module_request } for  pid=766 comm="hwclock" kmod="char-major-10-135" scontext=system_u:system_r:hwclock_t:s0 tcontext=system_u:system_r:kernel_t:s0 tclas
> 
> It turns out that the setpgid() system call fails to enter an RCU
> read-side critical section before doing a PID-to-task_struct translation.
> This commit therefore does rcu_read_lock() before the translation, and
> also does rcu_read_unlock() after the last use of the returned pointer.
> 
> Located-by: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
> 
>  sys.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/sys.c b/kernel/sys.c
> index e9ad444..05a4b0c 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -938,6 +938,7 @@ SYSCALL_DEFINE2(setpgid, pid_t, pid, pid_t, pgid)
>  	write_lock_irq(&tasklist_lock);
>  
>  	err = -ESRCH;
> +	rcu_read_lock();
>  	p = find_task_by_vpid(pid);

AFAICT the missing lock doesn't harm due to the write_lock of tasklist
above. But is probably a good thing to do anyway.

regards,
-- 
js
suse labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/