linux-kernel - Re: 2.6.19 file content corruption on ext3

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Date:	Thu, 21 Dec 2006 14:03:20 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Linus Torvalds <torvalds@...l.org>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...l.org>, andrei.popa@...eo.ro,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Hugh Dickins <hugh@...itas.com>,
	Florian Weimer <fw@...eb.enyo.de>,
	Marc Haber <mh+linux-kernel@...schlus.de>,
	Martin Michlmayr <tbm@...ius.com>
Subject: Re: 2.6.19 file content corruption on ext3

On Tue, 2006-12-19 at 09:43 -0800, Linus Torvalds wrote:
> 
> Btw,
>  here's a totally new tangent on this: it's possible that user code is 
> simply BUGGY. 

depmod: BADNESS: written outside isize 22183

---
diff --git a/fs/buffer.c b/fs/buffer.c
index d1f1b54..5db9fd9 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2393,6 +2393,17 @@ int nobh_commit_write(struct file *file, struct page *page,
 }
 EXPORT_SYMBOL(nobh_commit_write);
 
+static void __check_tail_zero(char *kaddr, unsigned int offset)
+{
+	unsigned int check = 0;
+	do {
+		check += kaddr[offset++];
+	} while (offset < PAGE_CACHE_SIZE);
+	if (check)
+		printk(KERN_ERR "%s: BADNESS: written outside isize %u\n",
+				current->comm, check);
+}
+
 /*
  * nobh_writepage() - based on block_full_write_page() except
  * that it tries to operate without attaching bufferheads to
@@ -2437,6 +2448,7 @@ int nobh_writepage(struct page *page, get_block_t *get_block,
 	 * writes to that region are not written out to the file."
 	 */
 	kaddr = kmap_atomic(page, KM_USER0);
+	__check_tail_zero(kaddr, offset);
 	memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
 	flush_dcache_page(page);
 	kunmap_atomic(kaddr, KM_USER0);
@@ -2604,6 +2616,7 @@ int block_write_full_page(struct page *page, get_block_t *get_block,
 	 * writes to that region are not written out to the file."
 	 */
 	kaddr = kmap_atomic(page, KM_USER0);
+	__check_tail_zero(kaddr, offset);
 	memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
 	flush_dcache_page(page);
 	kunmap_atomic(kaddr, KM_USER0);


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