[PATCH 19/36] scsi: Define usercopy region in scsi_sense_cache slab cache

[Kees Cook <keescook@xxxxxxxxxxxx>]

From: David Windsor <dave@xxxxxxxxxxxx>

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@xxxxxxxxxxxx>
[kees: adjust commit log, provide usage trace]
Cc: "James E.J. Bottomley" <jejb@xxxxxxxxxxxxxxxxxx>
Cc: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
Cc: linux-scsi@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 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