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    SubjectRe: Bad ext3/nfs DoS bug
    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
    -
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