linux-kernel - Re: [BLOCK] bh: Ensure bh fits within a page

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Date:	Wed, 02 Aug 2006 09:30:51 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	axboe@...e.de (Jens Axboe)
Cc:	herbert@...dor.apana.org.au, akpm@...l.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BLOCK] bh: Ensure bh fits within a page

Jens Axboe <axboe@...e.de> wrote:
>
> That looks really dangerous, I'd prefer that to be a BUG_ON() as well to
> prevent nastiness further down.

OK, I used a WARN_ON mainly because ext3 has been doing this for years
without killing anyone until now :)

[BLOCK] bh: Ensure bh fits within a page

There is a bug in jbd with slab debugging enabled where it was submitting
a bh obtained via jbd_rep_kmalloc which crossed a page boundary.  A lot
of time was spent on tracking this down because the symptoms were far off
from where the problem was.

This patch adds a sanity check to submit_bh so we can immediately spot
anyone doing similar things in future.

Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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--
diff --git a/fs/buffer.c b/fs/buffer.c
index 71649ef..ff34881 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2790,6 +2790,7 @@ int submit_bh(int rw, struct buffer_head
 	BUG_ON(!buffer_locked(bh));
 	BUG_ON(!buffer_mapped(bh));
 	BUG_ON(!bh->b_end_io);
+	BUG_ON(bh_offset(bh) + bh->b_size > PAGE_SIZE);
 
 	if (buffer_ordered(bh) && (rw == WRITE))
 		rw = WRITE_BARRIER;
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