linux-kernel - Re: Bad ext3/nfs DoS bug

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Message-ID: <17600.30372.397971.955987@cse.unsw.edu.au>
Date:	Fri, 21 Jul 2006 16:39:32 +1000
From:	Neil Brown <neilb@...e.de>
To:	Jan Kara <jack@...e.cz>
Cc:	James <20@...ingley.org>, Marcel Holtmann <marcel@...tmann.org>,
	linux-kernel@...r.kernel.org, akpm@...l.org, sct@...hat.com
Subject: Re: Bad ext3/nfs DoS bug

On Thursday July 20, jack@...e.cz wrote:
>   Yes, that looks fine too. I did not realize that we get the inode
> number only in a few places. Maybe we could wrap the checks in a
> function (possibly inline) so that the checks are just in one place?

Like this?

NeilBrown


Avoid triggering ext3_error on bad NFS file handle

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 a error,
then bad filehandles can have unpleasant effect.

So remove the call to ext3_error there and put a matching
check in ext3/namei.c where inode numbers are read of storage.

Signed-off-by: Neil Brown <neilb@...e.de>

### Diffstat output
 ./fs/ext3/inode.c         |   13 ++++++-------
 ./fs/ext3/namei.c         |   15 +++++++++++++--
 ./include/linux/ext3_fs.h |    9 +++++++++
 3 files changed, 28 insertions(+), 9 deletions(-)

diff .prev/fs/ext3/inode.c ./fs/ext3/inode.c
--- .prev/fs/ext3/inode.c	2006-07-20 14:41:07.000000000 +1000
+++ ./fs/ext3/inode.c	2006-07-21 16:36:32.000000000 +1000
@@ -2402,14 +2402,13 @@ static ext3_fsblk_t ext3_get_inode_block
 	struct buffer_head *bh;
 	struct ext3_group_desc * gdp;
 
-
-	if ((ino != EXT3_ROOT_INO && ino != EXT3_JOURNAL_INO &&
-		ino != EXT3_RESIZE_INO && ino < EXT3_FIRST_INO(sb)) ||
-		ino > le32_to_cpu(EXT3_SB(sb)->s_es->s_inodes_count)) {
-		ext3_error(sb, "ext3_get_inode_block",
-			    "bad inode number: %lu", ino);
+	if (!ext3_valid_inum(sb, ino))
+		/* This error already checked for in namei.c unless we
+		 * are looking at an NFS filehandle, in which case,
+		 * no error reported is needed
+		 */
 		return 0;
-	}
+
 	block_group = (ino - 1) / EXT3_INODES_PER_GROUP(sb);
 	if (block_group >= EXT3_SB(sb)->s_groups_count) {
 		ext3_error(sb,"ext3_get_inode_block","group >= groups count");

diff .prev/fs/ext3/namei.c ./fs/ext3/namei.c
--- .prev/fs/ext3/namei.c	2006-07-20 14:39:51.000000000 +1000
+++ ./fs/ext3/namei.c	2006-07-21 16:36:09.000000000 +1000
@@ -1000,7 +1000,12 @@ static struct dentry *ext3_lookup(struct
 	if (bh) {
 		unsigned long ino = le32_to_cpu(de->inode);
 		brelse (bh);
-		inode = iget(dir->i_sb, ino);
+		if (!ext3_valid_inum(dir->i_sb, ino)) {
+			ext3_error(dir->i_sb, "ext3_lookup",
+				   "bad inode number: %lu", ino);
+			inode = NULL;
+		} else
+			inode = iget(dir->i_sb, ino);
 
 		if (!inode)
 			return ERR_PTR(-EACCES);
@@ -1028,7 +1033,13 @@ struct dentry *ext3_get_parent(struct de
 		return ERR_PTR(-ENOENT);
 	ino = le32_to_cpu(de->inode);
 	brelse(bh);
-	inode = iget(child->d_inode->i_sb, ino);
+
+	if (!ext3_valid_inum(child->d_inode->i_sb, ino)) {
+		ext3_error(child->d_inode->i_sb, "ext3_get_parent",
+			   "bad inode number: %lu", ino);
+		inode = NULL;
+	} else
+		inode = iget(child->d_inode->i_sb, ino);
 
 	if (!inode)
 		return ERR_PTR(-EACCES);

diff .prev/include/linux/ext3_fs.h ./include/linux/ext3_fs.h
--- .prev/include/linux/ext3_fs.h	2006-07-21 16:34:01.000000000 +1000
+++ ./include/linux/ext3_fs.h	2006-07-21 16:35:55.000000000 +1000
@@ -492,6 +492,15 @@ static inline struct ext3_inode_info *EX
 {
 	return container_of(inode, struct ext3_inode_info, vfs_inode);
 }
+
+static inline int ext3_valid_inum(struct super_block *sb, unsigned long ino)
+{
+	return ino == EXT3_ROOT_INO ||
+		ino == EXT3_JOURNAL_INO ||
+		ino == EXT3_RESIZE_INO ||
+		(ino > EXT3_FIRST_INO(sb) &&
+		 ino <= le32_to_cpu(EXT3_SB(sb)->s_es->s_inodes_count));
+}
 #else
 /* Assume that user mode programs are passing in an ext3fs superblock, not
  * a kernel struct super_block.  This will allow us to call the feature-test
-
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