On Mon, Jan 08, 2018 at 11:13:36PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
>
> If a malicious filesystem image contains a block+ format directory
> wherein the directory inode's core.mode is set such that
> S_ISDIR(core.mode) == 0, and if there are subdirectories of the
> corrupted directory, an attempt to traverse up the directory tree will
> crash the kernel in __xfs_dir3_data_check. Running the online scrub's
> parent checks will tend to do this.
>
> The crash occurs because the directory inode's d_ops get set to
> xfs_dir[23]_nondir_ops (it's not a directory) but the parent pointer
> scrubber's indiscriminate call to xfs_readdir proceeds past the ASSERT
> if we have non fatal asserts configured.
>
> Fix the null pointer dereference crash in __xfs_dir3_data_check by
> looking for S_ISDIR or NULL data_entry_p; and teach the parent scrubber
> to bail out if it is fed a non-directory "parent".
>
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> ---
> fs/xfs/libxfs/xfs_dir2_data.c | 7 +++++++
> fs/xfs/scrub/parent.c | 2 +-
> 2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/libxfs/xfs_dir2_data.c b/fs/xfs/libxfs/xfs_dir2_data.c
> index 3237812..31d5ec6 100644
> --- a/fs/xfs/libxfs/xfs_dir2_data.c
> +++ b/fs/xfs/libxfs/xfs_dir2_data.c
> @@ -73,6 +73,13 @@ __xfs_dir3_data_check(
> */
> ops = xfs_dir_get_ops(mp, dp);
>
> + /*
> + * If this isn't a directory, or we got handed the non-dir ops,
> + * something is seriously wrong. Bail out.
> + */
> + if ((dp && !S_ISDIR(VFS_I(dp)->i_mode)) || !ops->data_entry_p)
> + return __this_address;
> +
I wonder if something like (ops == xfs_nondir_get_ops(mp, NULL)) would
be a bit more explicit for the second part of this check..? Otherwise
seems Ok to me.
Brian
> hdr = bp->b_addr;
> p = (char *)ops->data_entry_p(hdr);
>
> diff --git a/fs/xfs/scrub/parent.c b/fs/xfs/scrub/parent.c
> index dd704fd..0d38514 100644
> --- a/fs/xfs/scrub/parent.c
> +++ b/fs/xfs/scrub/parent.c
> @@ -171,7 +171,7 @@ xfs_scrub_parent_validate(
> error = xfs_iget(mp, sc->tp, dnum, 0, 0, &dp);
> if (!xfs_scrub_fblock_xref_process_error(sc, XFS_DATA_FORK, 0, &error))
> goto out;
> - if (dp == sc->ip) {
> + if (dp == sc->ip || !S_ISDIR(VFS_I(dp)->i_mode)) {
> xfs_scrub_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
> goto out_rele;
> }
> --
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