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    SubjectRe: [PATCH v2 15/30] xfs: Define usercopy region in xfs_inode slab cache
    On Mon, Aug 28, 2017 at 02:34:56PM -0700, Kees Cook wrote:
    > From: David Windsor <dave@nullcore.net>
    >
    > 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@nullcore.net>
    > [kees: adjust commit log, provide usage trace]
    > Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
    > Cc: linux-xfs@vger.kernel.org
    > Signed-off-by: Kees Cook <keescook@chromium.org>
    > ---
    > 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
    >
    > --
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