CVE-2016-6327 (C, published 2016-10-16T21:59Z)
Description: 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.
Severity: MEDIUM (CVSS v3 base score: 5.5)
Weakness: CWE-476 \u2014 NULL Pointer Dereference
The product dereferences a pointer that it expects to be valid but is NULL.
Repository: https://github.com/torvalds/linux
Files changed:
drivers/infiniband/ulp/srpt/ib_srpt.c
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>


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,