From: David Miller <davem@davemloft.net>
To: skb300@hotmail.com
Cc: linux-kernel@vger.kernel.org
Subject: Re: user pointers and race conditions
Date: Wed, 16 May 2007 22:06:31 -0700 (PDT) [thread overview]
Message-ID: <20070516.220631.07641650.davem@davemloft.net> (raw)
In-Reply-To: <BAY115-W33D3EC723171255D88FBF86330@phx.gbl>
From: sk b <skb300@hotmail.com>
Date: Wed, 16 May 2007 22:56:22 -0600
> 3: if (!access_ok(VERIFY_READ,stp,sizeof(struct st)))
> 4: return;
> 5: if (!access_ok(VERIFY_WRITE,stp->u,sizeof(int)))
> 6: return;
This code would not exist in the kernel, the kernel cannot dereference
stp->u. The stp->u dereference would silently work on x86 and x86_64
but it would generate an exception on sparc64 and other platforms.
User space accesses must go through the proper copy_from_user(),
copy_to_user, get_user(), and put_user() interfaces.
It must first copy stp into a local kernel space copy, then it may
inspect the value of stp->u.
And yes sparse would catch this problem in your code, because the
"__user" annotations would catch the illegal "stp->u" dereference.
next prev parent reply other threads:[~2007-05-17 5:06 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-17 4:56 sk b
2007-05-17 5:04 ` Al Viro
2007-05-17 5:06 ` David Miller [this message]
2007-05-17 12:26 ` Arjan van de Ven
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