Re: Bad ext3/nfs DoS bug

Neil Brown
2006-07-21T06:40:30Z

On Thursday July 20, jack@suse.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@suse.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