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    Subject[PATCH 19/36] scsi: Define usercopy region in scsi_sense_cache slab cache
    Date
    From: David Windsor <dave@nullcore.net>

    SCSI sense buffers, stored in struct scsi_cmnd.sense and therefore
    contained in the scsi_sense_cache slab cache, need to be copied to/from
    userspace.

    cache object allocation:
    drivers/scsi/scsi_lib.c:
    scsi_select_sense_cache(...):
    return ... ? scsi_sense_isadma_cache : scsi_sense_cache

    scsi_alloc_sense_buffer(...):
    return kmem_cache_alloc_node(scsi_select_sense_cache(), ...);

    scsi_init_request(...):
    ...
    cmd->sense_buffer = scsi_alloc_sense_buffer(...);
    ...
    cmd->req.sense = cmd->sense_buffer

    example usage trace:

    block/scsi_ioctl.c:
    (inline from sg_io)
    blk_complete_sghdr_rq(...):
    struct scsi_request *req = scsi_req(rq);
    ...
    copy_to_user(..., req->sense, len)

    scsi_cmd_ioctl(...):
    sg_io(...);

    In support of usercopy hardening, this patch defines a region in
    the scsi_sense_cache 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 dynamically sized copy operation involving
    cache-managed memory falls entirely within the slab's usercopy region.

    Signed-off-by: David Windsor <dave@nullcore.net>
    [kees: adjust commit log, provide usage trace]
    Cc: "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>
    Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
    Cc: linux-scsi@vger.kernel.org
    Signed-off-by: Kees Cook <keescook@chromium.org>
    ---
    drivers/scsi/scsi_lib.c | 9 +++++----
    1 file changed, 5 insertions(+), 4 deletions(-)

    diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
    index 1cbc497e00bd..164d062c4d94 100644
    --- a/drivers/scsi/scsi_lib.c
    +++ b/drivers/scsi/scsi_lib.c
    @@ -79,14 +79,15 @@ int scsi_init_sense_cache(struct Scsi_Host *shost)
    if (shost->unchecked_isa_dma) {
    scsi_sense_isadma_cache =
    kmem_cache_create("scsi_sense_cache(DMA)",
    - SCSI_SENSE_BUFFERSIZE, 0,
    - SLAB_HWCACHE_ALIGN | SLAB_CACHE_DMA, NULL);
    + SCSI_SENSE_BUFFERSIZE, 0,
    + SLAB_HWCACHE_ALIGN | SLAB_CACHE_DMA, NULL);
    if (!scsi_sense_isadma_cache)
    ret = -ENOMEM;
    } else {
    scsi_sense_cache =
    - kmem_cache_create("scsi_sense_cache",
    - SCSI_SENSE_BUFFERSIZE, 0, SLAB_HWCACHE_ALIGN, NULL);
    + kmem_cache_create_usercopy("scsi_sense_cache",
    + SCSI_SENSE_BUFFERSIZE, 0, SLAB_HWCACHE_ALIGN,
    + 0, SCSI_SENSE_BUFFERSIZE, NULL);
    if (!scsi_sense_cache)
    ret = -ENOMEM;
    }
    --
    2.7.4
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