CVE-2016-6327: NULL Pointer Dereference (CWE-476)
value: drivers/infiniband/ulp/srpt/ib_srpt.c in the Linux kernel before 4.5.1 allows local users to cause a denial of service (NULL pointer dereference and system crash) by using an ABORT_TASK command to abort a device write operation.
CWE description: The product dereferences a pointer that it expects to be valid but is NULL.
CVSS v3 base score: 5.5
Published: 2016-10-16T21:59Z
Repository: https://github.com/torvalds/linux
Language: C
Files changed: drivers/infiniband/ulp/srpt/ib_srpt.c
Commit date: 2016-02-29 17:12:34 -0500
Commit message: IB/srpt: Simplify srpt_handle_tsk_mgmt()

Let the target core check task existence instead of the SRP target
driver. Additionally, let the target core check the validity of the
task management request instead of the ib_srpt driver.

This patch fixes the following kernel crash:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000001
IP: [<ffffffffa0565f37>] srpt_handle_new_iu+0x6d7/0x790 [ib_srpt]
Oops: 0002 [#1] SMP
Call Trace:
 [<ffffffffa05660ce>] srpt_process_completion+0xde/0x570 [ib_srpt]
 [<ffffffffa056669f>] srpt_compl_thread+0x13f/0x160 [ib_srpt]
 [<ffffffff8109726f>] kthread+0xcf/0xe0
 [<ffffffff81613cfc>] ret_from_fork+0x7c/0xb0

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Fixes: 3e4f574857ee ("ib_srpt: Convert TMR path to target_submit_tmr")
Tested-by: Alex Estrin <alex.estrin@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>

Diff: diff --git a/drivers/infiniband/ulp/srpt/ib_srpt.c b/drivers/infiniband/ulp/srpt/ib_srpt.c
index 0c37fee363b1d..4328679a67a76 100644
--- a/drivers/infiniband/ulp/srpt/ib_srpt.c
+++ b/drivers/infiniband/ulp/srpt/ib_srpt.c
@@ -1668,51 +1668,10 @@ static int srpt_handle_cmd(struct srpt_rdma_ch *ch,
 send_sense:
 	transport_send_check_condition_and_sense(cmd, ret, 0);
 	return -1;
 }
 
-/**
- * srpt_rx_mgmt_fn_tag() - Process a task management function by tag.
- * @ch: RDMA channel of the task management request.
- * @fn: Task management function to perform.
- * @req_tag: Tag of the SRP task management request.
- * @mgmt_ioctx: I/O context of the task management request.
- *
- * Returns zero if the target core will process the task management
- * request asynchronously.
- *
- * Note: It is assumed that the initiator serializes tag-based task management
- * requests.
- */
-static int srpt_rx_mgmt_fn_tag(struct srpt_send_ioctx *ioctx, u64 tag)
-{
-	struct srpt_device *sdev;
-	struct srpt_rdma_ch *ch;
-	struct srpt_send_ioctx *target;
-	int ret, i;
-
-	ret = -EINVAL;
-	ch = ioctx->ch;
-	BUG_ON(!ch);
-	BUG_ON(!ch->sport);
-	sdev = ch->sport->sdev;
-	BUG_ON(!sdev);
-	spin_lock_irq(&sdev->spinlock);
-	for (i = 0; i < ch->rq_size; ++i) {
-		target = ch->ioctx_ring[i];
-		if (target->cmd.se_lun == ioctx->cmd.se_lun &&
-		    target->cmd.tag == tag &&
-		    srpt_get_cmd_state(target) != SRPT_STATE_DONE) {
-			ret = 0;
-			/* now let the target core abort &target->cmd; */
-			break;
-		}
-	}
-	spin_unlock_irq(&sdev->spinlock);
-	return ret;
-}
-
 static int srp_tmr_to_tcm(int fn)
 {
 	switch (fn) {
 	case SRP_TSK_ABORT_TASK:
 		return TMR_ABORT_TASK;
@@ -1743,11 +1702,10 @@ static void srpt_handle_tsk_mgmt(struct srpt_rdma_ch *ch,
 {
 	struct srp_tsk_mgmt *srp_tsk;
 	struct se_cmd *cmd;
 	struct se_session *sess = ch->sess;
 	uint64_t unpacked_lun;
-	uint32_t tag = 0;
 	int tcm_tmr;
 	int rc;
 
 	BUG_ON(!send_ioctx);
 
@@ -1759,29 +1717,14 @@ static void srpt_handle_tsk_mgmt(struct srpt_rdma_ch *ch,
 		 srp_tsk->task_tag, srp_tsk->tag, ch->cm_id, ch->sess);
 
 	srpt_set_cmd_state(send_ioctx, SRPT_STATE_MGMT);
 	send_ioctx->cmd.tag = srp_tsk->tag;
 	tcm_tmr = srp_tmr_to_tcm(srp_tsk->tsk_mgmt_func);
-	if (tcm_tmr < 0) {
-		send_ioctx->cmd.se_tmr_req->response =
-			TMR_TASK_MGMT_FUNCTION_NOT_SUPPORTED;
-		goto fail;
-	}
 	unpacked_lun = srpt_unpack_lun((uint8_t *)&srp_tsk->lun,
 				       sizeof(srp_tsk->lun));
-
-	if (srp_tsk->tsk_mgmt_func == SRP_TSK_ABORT_TASK) {
-		rc = srpt_rx_mgmt_fn_tag(send_ioctx, srp_tsk->task_tag);
-		if (rc < 0) {
-			send_ioctx->cmd.se_tmr_req->response =
-					TMR_TASK_DOES_NOT_EXIST;
-			goto fail;
-		}
-		tag = srp_tsk->task_tag;
-	}
 	rc = target_submit_tmr(&send_ioctx->cmd, sess, NULL, unpacked_lun,
-				srp_tsk, tcm_tmr, GFP_KERNEL, tag,
+				srp_tsk, tcm_tmr, GFP_KERNEL, srp_tsk->task_tag,
 				TARGET_SCF_ACK_KREF);
 	if (rc != 0) {
 		send_ioctx->cmd.se_tmr_req->response = TMR_FUNCTION_REJECTED;
 		goto fail;
 	}

Vulnerable code: /**
 * srpt_rx_mgmt_fn_tag() - Process a task management function by tag.
 * @ch: RDMA channel of the task management request.
 * @fn: Task management function to perform.
 * @req_tag: Tag of the SRP task management request.
 * @mgmt_ioctx: I/O context of the task management request.
 *
 * Returns zero if the target core will process the task management
 * request asynchronously.
 *
 * Note: It is assumed that the initiator serializes tag-based task management
 * requests.
 */
static int srpt_rx_mgmt_fn_tag(struct srpt_send_ioctx *ioctx, u64 tag)
{
	struct srpt_device *sdev;
	struct srpt_rdma_ch *ch;
	struct srpt_send_ioctx *target;
	int ret, i;

	ret = -EINVAL;
	ch = ioctx->ch;
	BUG_ON(!ch);
	BUG_ON(!ch->sport);
	sdev = ch->sport->sdev;
	BUG_ON(!sdev);
	spin_lock_irq(&sdev->spinlock);
	for (i = 0; i < ch->rq_size; ++i) {
		target = ch->ioctx_ring[i];
		if (target->cmd.se_lun == ioctx->cmd.se_lun &&
		    target->cmd.tag == tag &&
		    srpt_get_cmd_state(target) != SRPT_STATE_DONE) {
			ret = 0;
			/* now let the target core abort &target->cmd; */
			break;
		}
	}
	spin_unlock_irq(&sdev->spinlock);
	return ret;
}

	uint32_t tag = 0;
	if (tcm_tmr < 0) {
		send_ioctx->cmd.se_tmr_req->response =
			TMR_TASK_MGMT_FUNCTION_NOT_SUPPORTED;
		goto fail;
	}

	if (srp_tsk->tsk_mgmt_func == SRP_TSK_ABORT_TASK) {
		rc = srpt_rx_mgmt_fn_tag(send_ioctx, srp_tsk->task_tag);
		if (rc < 0) {
			send_ioctx->cmd.se_tmr_req->response =
					TMR_TASK_DOES_NOT_EXIST;
			goto fail;
		}
		tag = srp_tsk->task_tag;
	}
				srp_tsk, tcm_tmr, GFP_KERNEL, tag,
Fixed code: 				srp_tsk, tcm_tmr, GFP_KERNEL, srp_tsk->task_tag,