On Wed, Sep 21, 2022 at 10:44:55PM -0700, allison.henderson@xxxxxxxxxx wrote:
> From: Allison Henderson <allison.henderson@xxxxxxxxxx>
>
> Parent pointers returned to the get_fattr tool cause errors since
> the tool cannot parse parent pointers. Fix this by filtering parent
> parent pointers from xfs_attr_list.
Yes!! Parent pointers should /never/ be accessible by the standard VFS
xattr syscalls, nor should the XFS ATTR_MULTI calls handle them.
Changes to parent pointers are performed via separate syscalls
(link/unlink/mknod/creat/etc), and I see you've created a separate
parent pointer ioctl later on for userspace to retrieve them. I think
this is the correct access model.
To check that assertion -- getxattr/setxattr/removexattr (and the ATTRMULTI
equivalents) are prevented from accessing parent pointers directly
because you'd have to be able to set XFS_ATTR_PARENT in
xfs_da_args.attr_filter, right?
And for the VFS to get/set/remove a parent pointer, XFS would have to
provide a struct xattr_handler with ->flags = XFS_ATTR_PARENT, which XFS
will never do, right?
And for ATTR_MULTI to touch a parent pointer, xfs_attr_filter (and the
ioctl api) would have to learn about XFS_ATTR_PARENT, which XFS will
also never do, right?
If the answers to these three questions are all yes then you're 95% of
the way to an RVB, except...
> Signed-off-by: Allison Henderson <allison.henderson@xxxxxxxxxx>
> ---
> fs/xfs/libxfs/xfs_da_format.h | 3 +++
> fs/xfs/xfs_attr_list.c | 47 +++++++++++++++++++++++++++--------
> 2 files changed, 39 insertions(+), 11 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_da_format.h b/fs/xfs/libxfs/xfs_da_format.h
> index b02b67f1999e..e9c323fab6f3 100644
> --- a/fs/xfs/libxfs/xfs_da_format.h
> +++ b/fs/xfs/libxfs/xfs_da_format.h
> @@ -697,6 +697,9 @@ struct xfs_attr3_leafblock {
> #define XFS_ATTR_INCOMPLETE (1u << XFS_ATTR_INCOMPLETE_BIT)
> #define XFS_ATTR_NSP_ONDISK_MASK \
> (XFS_ATTR_ROOT | XFS_ATTR_SECURE | XFS_ATTR_PARENT)
> +#define XFS_ATTR_ALL \
> + (XFS_ATTR_LOCAL_BIT | XFS_ATTR_ROOT | XFS_ATTR_SECURE | \
> + XFS_ATTR_PARENT | XFS_ATTR_INCOMPLETE_BIT)
>
> /*
> * Alignment for namelist and valuelist entries (since they are mixed
> diff --git a/fs/xfs/xfs_attr_list.c b/fs/xfs/xfs_attr_list.c
> index a51f7f13a352..13de597c4996 100644
> --- a/fs/xfs/xfs_attr_list.c
> +++ b/fs/xfs/xfs_attr_list.c
> @@ -39,6 +39,23 @@ xfs_attr_shortform_compare(const void *a, const void *b)
> }
> }
>
> +/*
> + * Returns true or false if the parent attribute should be listed
> + */
> +static bool
> +xfs_attr_filter_parent(
> + struct xfs_attr_list_context *context,
> + int flags)
> +{
> + if (!(flags & XFS_ATTR_PARENT))
> + return true;
> +
> + if (context->attr_filter & XFS_ATTR_PARENT)
> + return true;
> +
> + return false;
...wouldn't it suffice to do:
static inline bool
xfs_attr_filter_listent(
struct xfs_attr_list_context *context,
int flags)
{
return context->attr_filter != (flags & XFS_ATTR_NSP_ONDISK_MASK);
}
like how xfs_ioc_attr_put_listent does? And then...
> +}
> +
> #define XFS_ISRESET_CURSOR(cursor) \
> (!((cursor)->initted) && !((cursor)->hashval) && \
> !((cursor)->blkno) && !((cursor)->offset))
> @@ -90,11 +107,12 @@ xfs_attr_shortform_list(
> sfe->namelen,
> sfe->flags)))
> return -EFSCORRUPTED;
> - context->put_listent(context,
> - sfe->flags,
> - sfe->nameval,
> - (int)sfe->namelen,
> - (int)sfe->valuelen);
> + if (xfs_attr_filter_parent(context, sfe->flags))
> + context->put_listent(context,
> + sfe->flags,
> + sfe->nameval,
> + (int)sfe->namelen,
> + (int)sfe->valuelen);
> /*
> * Either search callback finished early or
> * didn't fit it all in the buffer after all.
> @@ -185,11 +203,12 @@ xfs_attr_shortform_list(
> error = -EFSCORRUPTED;
> goto out;
> }
> - context->put_listent(context,
> - sbp->flags,
> - sbp->name,
> - sbp->namelen,
> - sbp->valuelen);
> + if (xfs_attr_filter_parent(context, sbp->flags))
> + context->put_listent(context,
> + sbp->flags,
> + sbp->name,
> + sbp->namelen,
> + sbp->valuelen);
> if (context->seen_enough)
> break;
> cursor->offset++;
> @@ -474,8 +493,10 @@ xfs_attr3_leaf_list_int(
> !xfs_attr_namecheck(mp, name, namelen,
> entry->flags)))
> return -EFSCORRUPTED;
> - context->put_listent(context, entry->flags,
> + if (xfs_attr_filter_parent(context, entry->flags))
> + context->put_listent(context, entry->flags,
> name, namelen, valuelen);
> +
> if (context->seen_enough)
> break;
> cursor->offset++;
> @@ -539,6 +560,10 @@ xfs_attr_list(
> if (xfs_is_shutdown(dp->i_mount))
> return -EIO;
>
> + if (context->attr_filter == 0)
> + context->attr_filter =
> + XFS_ATTR_ALL & ~XFS_ATTR_PARENT;
...I think this is unnecessary since none of the callers can actually
set XFS_ATTR_PARENT in the first place, right?
--D
> +
> lock_mode = xfs_ilock_attr_map_shared(dp);
> error = xfs_attr_list_ilocked(context);
> xfs_iunlock(dp, lock_mode);
> --
> 2.25.1
>
