linux-kernel - Re: [PATCH] add check do_direct

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Message-Id: <1185920712.31134.21.camel@dyn9047017100.beaverton.ibm.com>
Date:	Tue, 31 Jul 2007 15:25:11 -0700
From:	Badari Pulavarty <pbadari@...ibm.com>
To:	Joe Jin <joe.jin@...cle.com>
Cc:	Zach Brown <zach.brown@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	gurudas pai <gurudas.pai@...cle.com>,
	torvalds@...ux-foundation.org, jens.axboe@...cle.com,
	lkml <linux-kernel@...r.kernel.org>, wen.gang.wang@...cle.com
Subject: Re: [PATCH] add check do_direct_IO() return val

On Tue, 2007-07-31 at 12:35 +0800, Joe Jin wrote:
> > Hmm.. in this config file, whats causing DIO to panic ? Which test actually
> > passing faulty buffer ?
> > 
> 
> By my testing, just defined job3 and job10 will also get the panic, but if
> only have one of them, panic will not appear. the faulty buffer maybe passed
> by mmap.

Okay. Here is the fix for the problem.

Here is whats happening in this case:

Faulty user-buffer caused -EFAULT to be returned from do_direct_IO().
We go into dio_zero_block() to see if we need to zero out sections of
the block (if IO size < blocksize case). It checks if the buffer is
newly allocation by doing buffer_new(bh). map_bh is NOT initialized and
never went through get_block() code. So, its possible to pass the check
and end up submitting a page wrongly and causing the oops.

Fix is to initialize the buffer state. 

Thanks,
Badari

Need to initialize map_bh.b_state to zero. Otherwise, in case of
a faulty user-buffer its possible to go into dio_zero_block()
and submit a page by mistake - since it checks for buffer_new().

http://marc.info/?l=linux-kernel&m=118551339032528&w=2

Signed-off-by: Badari Pulavarty <pbadari@...ibm.com>
---
 fs/direct-io.c |    1 +
 1 file changed, 1 insertion(+)

Index: linux-2.6.23-rc1/fs/direct-io.c
===================================================================
--- linux-2.6.23-rc1.orig/fs/direct-io.c	2007-07-22 13:41:00.000000000 -0700
+++ linux-2.6.23-rc1/fs/direct-io.c	2007-07-31 15:13:44.000000000 -0700
@@ -974,6 +974,7 @@ direct_io_worker(int rw, struct kiocb *i
 	dio->get_block = get_block;
 	dio->end_io = end_io;
 	dio->map_bh.b_private = NULL;
+	dio->map_bh.b_state = 0;
 	dio->final_block_in_bio = -1;
 	dio->next_block_for_io = -1;
 


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