linux-kernel - Re: [PATCH 1/1] ramfs/nommu: fix bug - kernel crash when (nr != lpages)

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Date:	Thu, 08 Jan 2009 10:58:53 +0000
From:	David Howells <dhowells@...hat.com>
To:	Bryan Wu <cooloney@...nel.org>, Graf Yang <graf.yang@...log.com>
Cc:	dhowells@...hat.com, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 1/1] ramfs/nommu: fix bug - kernel crash when (nr != lpages)


Bryan Wu <cooloney@...nel.org> wrote:

> Avoiding kernel crash when (nr != lpages), and return -ENOMEM,
> let the user space application handle this error.

A better patch is attached.

David
---
From: David Howells <dhowells@...hat.com>
Subject: [PATCH] NOMMU: Fix cleanup handling in ramfs_nommu_get_umapped_area()

Fix cleanup handling in ramfs_nommu_get_umapped_area() by only freeing the
number of pages that find_get_pages() said it had returned (nr) rather than
attempting to free the number of pages we asked for (lpages) - thus avoiding
the situation whereby put_page() may be handed NULL pointers if
find_get_pages() returned fewer pages that were requested.

Also avoid a warning about nr being uninitialised and the need for an
if-statement in the cleanup path by using appropriate gotos.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 fs/ramfs/file-nommu.c |   21 ++++++++++-----------
 1 files changed, 10 insertions(+), 11 deletions(-)


diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c
index 76acdbc..b9b567a 100644
--- a/fs/ramfs/file-nommu.c
+++ b/fs/ramfs/file-nommu.c
@@ -262,11 +262,11 @@ unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
 	ret = -ENOMEM;
 	pages = kzalloc(lpages * sizeof(struct page *), GFP_KERNEL);
 	if (!pages)
-		goto out;
+		goto out_free;
 
 	nr = find_get_pages(inode->i_mapping, pgoff, lpages, pages);
 	if (nr != lpages)
-		goto out; /* leave if some pages were missing */
+		goto out_free_pages; /* leave if some pages were missing */
 
 	/* check the pages for physical adjacency */
 	ptr = pages;
@@ -274,19 +274,18 @@ unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
 	page++;
 	for (loop = lpages; loop > 1; loop--)
 		if (*ptr++ != page++)
-			goto out;
+			goto out_free_pages;
 
 	/* okay - all conditions fulfilled */
 	ret = (unsigned long) page_address(pages[0]);
 
- out:
-	if (pages) {
-		ptr = pages;
-		for (loop = lpages; loop > 0; loop--)
-			put_page(*ptr++);
-		kfree(pages);
-	}
-
+out_free_pages:
+	ptr = pages;
+	for (loop = nr; loop > 0; loop--)
+		put_page(*ptr++);
+out_free:
+	kfree(pages);
+out:
 	return ret;
 }
 
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