[PATCH 10/31] Avoid that scsi_exit_rq() triggers a use-after-free

Bart Van Assche
2017-05-24T00:33:59Z

Dereferencing shost from scsi_exit_rq() is not safe because the
SCSI host may already have been freed when scsi_exit_rq() is
called. Increasing the shost reference count in scsi_init_rq()
and dropping that reference in scsi_exit_rq() is nontrivial since
scsi_host_dev_release() may sleep and since scsi_exit_rq() may
be called from interrupt context. Since scsi_exit_rq() only needs
a single bit from shost, copy that bit into struct scsi_cmnd.

Reported-by: Scott Bauer <scott.bauer@intel.com>
Fixes: e9c787e65c0c ("scsi: allocate scsi_cmnd structures as part of struct request")
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Scott Bauer <scott.bauer@intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jan Kara <jack@suse.cz>
Cc: Hannes Reinecke <hare@suse.com>
Cc: <stable@vger.kernel.org>
---
drivers/scsi/scsi_lib.c | 43 +++++++++++++++++++++++++------------------
include/scsi/scsi_cmnd.h | 1 +
2 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 30a7900d331c..59400033aba8 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -44,23 +44,23 @@ static struct kmem_cache *scsi_sense_isadma_cache;
static DEFINE_MUTEX(scsi_sense_cache_mutex);

static inline struct kmem_cache *
-scsi_select_sense_cache(struct Scsi_Host *shost)
+scsi_select_sense_cache(bool unchecked_isa_dma)
{
- return shost->unchecked_isa_dma ?
- scsi_sense_isadma_cache : scsi_sense_cache;
+ return unchecked_isa_dma ? scsi_sense_isadma_cache : scsi_sense_cache;
}

-static void scsi_free_sense_buffer(struct Scsi_Host *shost,
- unsigned char *sense_buffer)
+static void scsi_free_sense_buffer(bool unchecked_isa_dma,
+ unsigned char *sense_buffer)
{
- kmem_cache_free(scsi_select_sense_cache(shost), sense_buffer);
+ kmem_cache_free(scsi_select_sense_cache(unchecked_isa_dma),
+ sense_buffer);
}

-static unsigned char *scsi_alloc_sense_buffer(struct Scsi_Host *shost,
+static unsigned char *scsi_alloc_sense_buffer(bool unchecked_isa_dma,
gfp_t gfp_mask, int numa_node)
{
- return kmem_cache_alloc_node(scsi_select_sense_cache(shost), gfp_mask,
- numa_node);
+ return kmem_cache_alloc_node(scsi_select_sense_cache(unchecked_isa_dma),
+ gfp_mask, numa_node);
}

int scsi_init_sense_cache(struct Scsi_Host *shost)
@@ -68,7 +68,7 @@ int scsi_init_sense_cache(struct Scsi_Host *shost)
struct kmem_cache *cache;
int ret = 0;

- cache = scsi_select_sense_cache(shost);
+ cache = scsi_select_sense_cache(shost->unchecked_isa_dma);
if (cache)
return 0;

@@ -2003,10 +2003,13 @@ static int scsi_init_request(struct blk_mq_tag_set *set, struct request *rq,
unsigned int hctx_idx, unsigned int numa_node)
{
struct Scsi_Host *shost = set->driver_data;
+ const bool unchecked_isa_dma = shost->unchecked_isa_dma;
struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);

- cmd->sense_buffer =
- scsi_alloc_sense_buffer(shost, GFP_KERNEL, numa_node);
+ if (unchecked_isa_dma)
+ cmd->flags |= SCMD_UNCHECKED_ISA_DMA;
+ cmd->sense_buffer = scsi_alloc_sense_buffer(unchecked_isa_dma,
+ GFP_KERNEL, numa_node);
if (!cmd->sense_buffer)
return -ENOMEM;
cmd->req.sense = cmd->sense_buffer;
@@ -2016,10 +2019,10 @@ static int scsi_init_request(struct blk_mq_tag_set *set, struct request *rq,
static void scsi_exit_request(struct blk_mq_tag_set *set, struct request *rq,
unsigned int hctx_idx)
{
- struct Scsi_Host *shost = set->driver_data;
struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);

- scsi_free_sense_buffer(shost, cmd->sense_buffer);
+ scsi_free_sense_buffer(cmd->flags & SCMD_UNCHECKED_ISA_DMA,
+ cmd->sense_buffer);
}

static int scsi_map_queues(struct blk_mq_tag_set *set)
@@ -2092,11 +2095,15 @@ EXPORT_SYMBOL_GPL(__scsi_init_queue);
static int scsi_init_rq(struct request_queue *q, struct request *rq, gfp_t gfp)
{
struct Scsi_Host *shost = q->rq_alloc_data;
+ const bool unchecked_isa_dma = shost->unchecked_isa_dma;
struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);

memset(cmd, 0, sizeof(*cmd));

- cmd->sense_buffer = scsi_alloc_sense_buffer(shost, gfp, NUMA_NO_NODE);
+ if (unchecked_isa_dma)
+ cmd->flags |= SCMD_UNCHECKED_ISA_DMA;
+ cmd->sense_buffer = scsi_alloc_sense_buffer(unchecked_isa_dma, gfp,
+ NUMA_NO_NODE);
if (!cmd->sense_buffer)
goto fail;
cmd->req.sense = cmd->sense_buffer;
@@ -2110,19 +2117,19 @@ static int scsi_init_rq(struct request_queue *q, struct request *rq, gfp_t gfp)
return 0;

fail_free_sense:
- scsi_free_sense_buffer(shost, cmd->sense_buffer);
+ scsi_free_sense_buffer(unchecked_isa_dma, cmd->sense_buffer);
fail:
return -ENOMEM;
}

static void scsi_exit_rq(struct request_queue *q, struct request *rq)
{
- struct Scsi_Host *shost = q->rq_alloc_data;
struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq);

if (cmd->prot_sdb)
kmem_cache_free(scsi_sdb_cache, cmd->prot_sdb);
- scsi_free_sense_buffer(shost, cmd->sense_buffer);
+ scsi_free_sense_buffer(cmd->flags & SCMD_UNCHECKED_ISA_DMA,
+ cmd->sense_buffer);
}

struct request_queue *scsi_alloc_queue(struct scsi_device *sdev)
diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index b379f93a2c48..16351de31243 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -56,6 +56,7 @@ struct scsi_pointer {

/* for scmd->flags */
#define SCMD_TAGGED (1 << 0)
+#define SCMD_UNCHECKED_ISA_DMA (1 << 1)

struct scsi_cmnd {
struct scsi_request req;
--
2.12.2