linux-kernel - Re: [patch 16/23] ext3: avoid triggering ext3

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Date:	Fri, 04 Aug 2006 10:35:34 -0500
From:	Eric Sandeen <esandeen@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>,
	Eric Sandeen <esandeen@...hat.com>, Greg KH <gregkh@...e.de>,
	linux-kernel@...r.kernel.org, stable@...nel.org, torvalds@...l.org,
	Justin Forbes <jmforbes@...uxtx.org>,
	Zwane Mwaikambo <zwane@....linux.org.uk>,
	"Theodore Ts'o" <tytso@....edu>,
	Randy Dunlap <rdunlap@...otime.net>,
	Dave Jones <davej@...hat.com>,
	Chuck Wolber <chuckw@...ntumlinux.com>,
	Chris Wedgwood <reviews@...cw.f00f.org>, akpm@...l.org,
	alan@...rguk.ukuu.org.uk, jack@...e.cz, neilb@...e.de,
	Marcel Holtmann <marcel@...tmann.org>,
	"Stephen C. Tweedie" <sct@...hat.com>
Subject: Re: [patch 16/23] ext3: avoid triggering ext3_error on bad NFS file
 handle

Christoph Hellwig wrote:
> On Fri, Aug 04, 2006 at 09:45:52AM -0500, Eric Sandeen wrote:
>> Greg KH wrote:
>>> -stable review patch.  If anyone has any objections, please let us know.
>>>
>>> ------------------
>>> From: Neil Brown <neilb@...e.de>
>>>
>>> The inode number out of an NFS file handle gets passed eventually to
>>> ext3_get_inode_block() without any checking.  If ext3_get_inode_block()
>>> allows it to trigger an error, then bad filehandles can have unpleasant
>>> effect - ext3_error() will usually cause a forced read-only remount, or a
>>> panic if `errors=panic' was used.
>>>
>>> So remove the call to ext3_error there and put a matching check in
>>> ext3/namei.c where inode numbers are read off storage.
>> This patch and the ext2 patch (23/23) are accomplishing the same thing in 2 
>> different ways, I think, and introducing unnecessary differences between 
>> ext2 and ext3.  I'd personally prefer to see both ext2 and ext3 handled 
>> with the get_dentry op addition, and I'd be happy to quickly whip up the 
>> ext3 patch to do this if there's agreement on this path.
> 
> I completly agree with Eric here.  Also pushing out only the fix for one
> (and today probably the lesser used) filesystems to -stable seems wrong.

so how's this? (compile tested)

Thanks,
-Eric

Signed-off-by: Eric Sandeen <sandeen@...deen.net>

(tho blatantly ripped off from Neil Brown's ext2 patch)

Index: linux-2.6.17/fs/ext3/super.c
===================================================================
--- linux-2.6.17.orig/fs/ext3/super.c
+++ linux-2.6.17/fs/ext3/super.c
@@ -620,8 +620,48 @@ static struct super_operations ext3_sops
 #endif
 };
 
+static struct dentry *ext3_get_dentry(struct super_block *sb, void *vobjp)
+{
+	__u32 *objp = vobjp;
+	unsigned long ino = objp[0];
+	__u32 generation = objp[1];
+	struct inode *inode;
+	struct dentry *result;
+
+	if (ino != EXT3_ROOT_INO && ino < EXT3_FIRST_INO(sb))
+		return ERR_PTR(-ESTALE);
+	if (ino > le32_to_cpu(EXT3_SB(sb)->s_es->s_inodes_count))
+		return ERR_PTR(-ESTALE);
+
+	/* iget isn't really right if the inode is currently unallocated!!
+	 * ext3_read_inode currently does appropriate checks, but
+	 * it might be "neater" to call ext3_get_inode first and check
+	 * if the inode is valid.....
+	 */
+	inode = iget(sb, ino);
+	if (inode == NULL)
+		return ERR_PTR(-ENOMEM);
+	if (is_bad_inode(inode)
+	    || (generation && inode->i_generation != generation)
+		) {
+		/* we didn't find the right inode.. */
+		iput(inode);
+		return ERR_PTR(-ESTALE);
+	}
+	/* now to find a dentry.
+	 * If possible, get a well-connected one
+	 */
+	result = d_alloc_anon(inode);
+	if (!result) {
+		iput(inode);
+		return ERR_PTR(-ENOMEM);
+	}
+	return result;
+}
+
 static struct export_operations ext3_export_ops = {
 	.get_parent = ext3_get_parent,
+	.get_dentry = ext3_get_dentry,
 };
 
 enum {