Re: Bad ext3/nfs DoS bug

Jan Kara
2006-07-21T14:24:00Z

> 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?
Yes.

> 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>
Signed-off-by: Jan Kara <jack@suse.cz>

Honza

> ### 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
--
Jan Kara <jack@suse.cz>
SuSE CR Labs