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Commit 057085e5 authored by Nicholas Bellinger's avatar Nicholas Bellinger
Browse files

target: Fix race for SCF_COMPARE_AND_WRITE_POST checking 



This patch addresses a race + use after free where the first
stage of COMPARE_AND_WRITE in compare_and_write_callback()
is rescheduled after the backend sends the secondary WRITE,
resulting in second stage compare_and_write_post() callback
completing in target_complete_ok_work() before the first
can return.

Because current code depends on checking se_cmd->se_cmd_flags
after return from se_cmd->transport_complete_callback(),
this results in first stage having SCF_COMPARE_AND_WRITE_POST
set, which incorrectly falls through into second stage CAW
processing code, eventually triggering a NULL pointer
dereference due to use after free.

To address this bug, pass in a new *post_ret parameter into
se_cmd->transport_complete_callback(), and depend upon this
value instead of ->se_cmd_flags to determine when to return
or fall through into ->queue_status() code for CAW.

Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: <stable@vger.kernel.org> # v3.12+
Signed-off-by: default avatarNicholas Bellinger <nab@linux-iscsi.org>
parent ca82c2bd

drivers/target/target_core_sbc.c

+9 −4
Original line number Diff line number Diff line
@@ -371,7 +371,8 @@ sbc_setup_write_same(struct se_cmd *cmd, unsigned char *flags, struct sbc_ops *o 
	return 0;

}



static sense_reason_t xdreadwrite_callback(struct se_cmd *cmd, bool success)

static sense_reason_t xdreadwrite_callback(struct se_cmd *cmd, bool success,

					   int *post_ret)

{

	unsigned char *buf, *addr;

	struct scatterlist *sg;
@@ -437,7 +438,8 @@ sbc_execute_rw(struct se_cmd *cmd) 
			       cmd->data_direction);

}



static sense_reason_t compare_and_write_post(struct se_cmd *cmd, bool success)

static sense_reason_t compare_and_write_post(struct se_cmd *cmd, bool success,

					     int *post_ret)

{

	struct se_device *dev = cmd->se_dev;
@@ -447,8 +449,10 @@ static sense_reason_t compare_and_write_post(struct se_cmd *cmd, bool success) 
	 * sent to the backend driver.

	 */

	spin_lock_irq(&cmd->t_state_lock);

	if ((cmd->transport_state & CMD_T_SENT) && !cmd->scsi_status)

	if ((cmd->transport_state & CMD_T_SENT) && !cmd->scsi_status) {

		cmd->se_cmd_flags |= SCF_COMPARE_AND_WRITE_POST;

		*post_ret = 1;

	}

	spin_unlock_irq(&cmd->t_state_lock);



	/*
@@ -460,7 +464,8 @@ static sense_reason_t compare_and_write_post(struct se_cmd *cmd, bool success) 
	return TCM_NO_SENSE;

}



static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool success)

static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool success,

						 int *post_ret)

{

	struct se_device *dev = cmd->se_dev;

	struct scatterlist *write_sg = NULL, *sg;

drivers/target/target_core_transport.c

+8 −6
Original line number Diff line number Diff line
@@ -1658,7 +1658,7 @@ bool target_stop_cmd(struct se_cmd *cmd, unsigned long *flags) 
void transport_generic_request_failure(struct se_cmd *cmd,

		sense_reason_t sense_reason)

{

	int ret = 0;

	int ret = 0, post_ret = 0;



	pr_debug("-----[ Storage Engine Exception for cmd: %p ITT: 0x%08llx"

		" CDB: 0x%02x\n", cmd, cmd->tag, cmd->t_task_cdb[0]);
@@ -1680,7 +1680,7 @@ void transport_generic_request_failure(struct se_cmd *cmd, 
	 */

	if ((cmd->se_cmd_flags & SCF_COMPARE_AND_WRITE) &&

	     cmd->transport_complete_callback)

		cmd->transport_complete_callback(cmd, false);

		cmd->transport_complete_callback(cmd, false, &post_ret);



	switch (sense_reason) {

	case TCM_NON_EXISTENT_LUN:
@@ -2068,11 +2068,13 @@ static void target_complete_ok_work(struct work_struct *work) 
	 */

	if (cmd->transport_complete_callback) {

		sense_reason_t rc;

		bool caw = (cmd->se_cmd_flags & SCF_COMPARE_AND_WRITE);

		bool zero_dl = !(cmd->data_length);

		int post_ret = 0;



		rc = cmd->transport_complete_callback(cmd, true);

		if (!rc && !(cmd->se_cmd_flags & SCF_COMPARE_AND_WRITE_POST)) {

			if ((cmd->se_cmd_flags & SCF_COMPARE_AND_WRITE) &&

			    !cmd->data_length)

		rc = cmd->transport_complete_callback(cmd, true, &post_ret);

		if (!rc && !post_ret) {

			if (caw && zero_dl)

				goto queue_rsp;



			return;

include/target/target_core_base.h

+1 −1
Original line number Diff line number Diff line
@@ -474,7 +474,7 @@ struct se_cmd { 
	struct completion	cmd_wait_comp;

	const struct target_core_fabric_ops *se_tfo;

	sense_reason_t		(*execute_cmd)(struct se_cmd *);

	sense_reason_t (*transport_complete_callback)(struct se_cmd *, bool);

	sense_reason_t (*transport_complete_callback)(struct se_cmd *, bool, int *);

	void			*protocol_data;



	unsigned char		*t_task_cdb;