On Mon, Aug 28, 2017 at 02:34:56PM -0700, Kees Cook wrote:
> From: David Windsor <dave@xxxxxxxxxxxx>
>
> The XFS inline inode data, stored in struct xfs_inode_t field
> i_df.if_u2.if_inline_data and therefore contained in the xfs_inode slab
> cache, needs to be copied to/from userspace.
>
> cache object allocation:
> fs/xfs/xfs_icache.c:
> xfs_inode_alloc(...):
> ...
> ip = kmem_zone_alloc(xfs_inode_zone, KM_SLEEP);
>
> fs/xfs/libxfs/xfs_inode_fork.c:
> xfs_init_local_fork(...):
> ...
> if (mem_size <= sizeof(ifp->if_u2.if_inline_data))
> ifp->if_u1.if_data = ifp->if_u2.if_inline_data;
Hmm, what happens when mem_size > sizeof(if_inline_data)? A slab object
will be allocated for ifp->if_u1.if_data which can then be used for
readlink in the same manner as the example usage trace below. Does
that allocated object have a need for a usercopy annotation like
the one we're adding for if_inline_data? Or is that already covered
elsewhere?
--D
> ...
>
> fs/xfs/xfs_symlink.c:
> xfs_symlink(...):
> ...
> xfs_init_local_fork(ip, XFS_DATA_FORK, target_path, pathlen);
>
> example usage trace:
> readlink_copy+0x43/0x70
> vfs_readlink+0x62/0x110
> SyS_readlinkat+0x100/0x130
>
> fs/xfs/xfs_iops.c:
> (via inode->i_op->get_link)
> xfs_vn_get_link_inline(...):
> ...
> return XFS_I(inode)->i_df.if_u1.if_data;
>
> fs/namei.c:
> readlink_copy(..., link):
> ...
> copy_to_user(..., link, len);
>
> generic_readlink(dentry, ...):
> struct inode *inode = d_inode(dentry);
> const char *link = inode->i_link;
> ...
> if (!link) {
> link = inode->i_op->get_link(dentry, inode, &done);
> ...
> readlink_copy(..., link);
>
> In support of usercopy hardening, this patch defines a region in the
> xfs_inode slab cache in which userspace copy operations are allowed.
>
> This region is known as the slab cache's usercopy region. Slab caches can
> now check that each copy operation involving cache-managed memory falls
> entirely within the slab's usercopy region.
>
> This patch is modified from Brad Spengler/PaX Team's PAX_USERCOPY
> whitelisting code in the last public patch of grsecurity/PaX based on my
> understanding of the code. Changes or omissions from the original code are
> mine and don't reflect the original grsecurity/PaX code.
>
> Signed-off-by: David Windsor <dave@xxxxxxxxxxxx>
> [kees: adjust commit log, provide usage trace]
> Cc: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
> Cc: linux-xfs@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> fs/xfs/kmem.h | 10 ++++++++++
> fs/xfs/xfs_super.c | 7 +++++--
> 2 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/fs/xfs/kmem.h b/fs/xfs/kmem.h
> index 4d85992d75b2..08358f38dee6 100644
> --- a/fs/xfs/kmem.h
> +++ b/fs/xfs/kmem.h
> @@ -110,6 +110,16 @@ kmem_zone_init_flags(int size, char *zone_name, unsigned long flags,
> return kmem_cache_create(zone_name, size, 0, flags, construct);
> }
>
> +static inline kmem_zone_t *
> +kmem_zone_init_flags_usercopy(int size, char *zone_name, unsigned long flags,
> + size_t useroffset, size_t usersize,
> + void (*construct)(void *))
> +{
> + return kmem_cache_create_usercopy(zone_name, size, 0, flags,
> + useroffset, usersize, construct);
> +}
> +
> +
> static inline void
> kmem_zone_free(kmem_zone_t *zone, void *ptr)
> {
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 38aaacdbb8b3..6ca428c6f943 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -1829,9 +1829,12 @@ xfs_init_zones(void)
> goto out_destroy_efd_zone;
>
> xfs_inode_zone =
> - kmem_zone_init_flags(sizeof(xfs_inode_t), "xfs_inode",
> + kmem_zone_init_flags_usercopy(sizeof(xfs_inode_t), "xfs_inode",
> KM_ZONE_HWALIGN | KM_ZONE_RECLAIM | KM_ZONE_SPREAD |
> - KM_ZONE_ACCOUNT, xfs_fs_inode_init_once);
> + KM_ZONE_ACCOUNT,
> + offsetof(xfs_inode_t, i_df.if_u2.if_inline_data),
> + sizeof_field(xfs_inode_t, i_df.if_u2.if_inline_data),
> + xfs_fs_inode_init_once);
> if (!xfs_inode_zone)
> goto out_destroy_efi_zone;
>
> --
> 2.7.4
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
