linux-kernel - Re: [PATCH] jffs2: Fix memory corruption in jffs2_read_inode

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Date:	Sun, 22 Nov 2009 10:20:59 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	Anton Vorontsov <avorontsov@...mvista.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Neil Brown <neilb@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>
Subject: Re: [PATCH] jffs2: Fix memory corruption in
 jffs2_read_inode_range()

On Fri, 2009-11-20 at 12:45 -0700, Anton Vorontsov wrote:
> +       if (pg->index > ((i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT)) {
> +               ret = 0;
> +               memset(pg_buf, 0, PAGE_CACHE_SIZE);
> +       } else {
> +               ret = jffs2_read_inode_range(c, f, pg_buf,
> +                       pg->index << PAGE_CACHE_SHIFT, PAGE_CACHE_SIZE);
> +       } 

Thank you for the excellent diagnosis and the patch. 

I think I'd prefer to fix it a little differently though -- I would be
happier to make jffs2_read_inode_range() cope with out-of-file reads,
rather than adding this special case where we don't call it.

That way we aren't at all susceptible to potential races between the
VFS-maintained i_size and our own internal fragtree handling. And
jffs2_read_inode_range() already handles the memset to zero for various
other reasons anyway.

Does this patch look OK to you? It seems to work on the test cases I've
tried.

diff --git a/fs/jffs2/read.c b/fs/jffs2/read.c
index cfe05c1..9640175 100644
--- a/fs/jffs2/read.c
+++ b/fs/jffs2/read.c
@@ -164,12 +164,14 @@ int jffs2_read_inode_range(struct jffs2_sb_info *c, struct jffs2_inode_info *f,
 
 	/* XXX FIXME: Where a single physical node actually shows up in two
 	   frags, we read it twice. Don't do that. */
-	/* Now we're pointing at the first frag which overlaps our page */
+	/* Now we're pointing at the first frag which overlaps our page
+	 * (or perhaps is before it, if we've been asked to read off the
+	 * end of the file). */
 	while(offset < end) {
 		D2(printk(KERN_DEBUG "jffs2_read_inode_range: offset %d, end %d\n", offset, end));
-		if (unlikely(!frag || frag->ofs > offset)) {
+		if (unlikely(!frag || frag->ofs > offset || frag->ofs + frag->size <= offset)) {
 			uint32_t holesize = end - offset;
-			if (frag) {
+			if (frag && frag->ofs > offset) {
 				D1(printk(KERN_NOTICE "Eep. Hole in ino #%u fraglist. frag->ofs = 0x%08x, offset = 0x%08x\n", f->inocache->ino, frag->ofs, offset));
 				holesize = min(holesize, frag->ofs - offset);
 			}


-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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