netdev - Re: [PATCH] netlink: fix locking around NETLINK_LIST

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Message-Id: <20151022.071910.1647968553018138414.davem@davemloft.net>
Date:	Thu, 22 Oct 2015 07:19:10 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	dh.herrmann@...il.com
Cc:	netdev@...r.kernel.org, dvyukov@...gle.com, edumazet@...gle.com,
	torvalds@...ux-foundation.org, stable@...r.kernel.org
Subject: Re: [PATCH] netlink: fix locking around NETLINK_LIST_MEMBERSHIPS

From: David Herrmann <dh.herrmann@...il.com>
Date: Wed, 21 Oct 2015 11:47:43 +0200

> Currently, NETLINK_LIST_MEMBERSHIPS grabs the netlink table while copying
> the membership state to user-space. However, grabing the netlink table is
> effectively a write_lock_irq(), and as such we should not be triggering
> page-faults in the critical section.
> 
> This can be easily reproduced by the following snippet:
>     int s = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
>     void *p = mmap(0, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0);
>     int r = getsockopt(s, 0x10e, 9, p, (void*)((char*)p + 4092));
> 
> This should work just fine, but currently triggers EFAULT and a possible
> WARN_ON below handle_mm_fault().
> 
> Fix this by reducing locking of NETLINK_LIST_MEMBERSHIPS to a read-side
> lock. The write-lock was overkill in the first place, and the read-lock
> allows page-faults just fine.
> 
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: David Herrmann <dh.herrmann@...il.com>

Applied and queued up for -stable, thanks.
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