linux-kernel - [PATCH] kexec: segmentation fault in kimage_add

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Message-ID: <m1d4j3g29q.fsf@frodo.ebiederm.org>
Date:	Tue, 16 Sep 2008 15:21:53 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Jonathan Steel <jon.steel@...ntire.com>
Subject: [PATCH] kexec: segmentation fault in kimage_add_entry

From: Jonathan Steel <jon.steel@...ntire.com>

A segmentation fault can occur in kimage_add_entry in kexec.c when
loading a kernel image into memory. The fault occurs because a page is
requested by calling kimage_alloc_page with gfp_mask GFP_KERNEL and the
function may actually return a page with gfp_mask GFP_HIGHUSER. The high
mem page is returned because it was swapped with the kernel page due to
the kernel page being a page that will shortly be copied to.

This patch ensures that kimage_alloc_page returns a page that was
created with the correct gfp flags.

I have verified the change and fixed the whitespace damage of the
original patch.  Jonathan did a great job of tracking this down
after he hit the problem. -- Eric

Signed-off-by: Jonathan Steel <jon.steel@...ntire.com>
Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
---
 kernel/kexec.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/kernel/kexec.c b/kernel/kexec.c
index 59f3f0d..aef2653 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -753,8 +753,14 @@ static struct page *kimage_alloc_page(struct kimage *image,
 			*old = addr | (*old & ~PAGE_MASK);

 			/* The old page I have found cannot be a
-			 * destination page, so return it.
+			 * destination page, so return it if it's
+			 * gfp_flags honor the ones passed in.
 			 */
+			if (!(gfp_mask & __GFP_HIGHMEM) &&
+			    PageHighMem(old_page)) {
+				kimage_free_pages(old_page);
+				continue;
+			}
 			addr = old_addr;
 			page = old_page;
 			break;
-- 
1.5.3.rc6.17.g1911

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