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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: Nicholas Bellinger <nab@linux-iscsi.org>
This commit is contained in:
Nicholas Bellinger 2015-11-05 23:37:59 -08:00
parent ca82c2bded
commit 057085e522
3 changed files with 18 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
drivers/target/target_core_sbc.c
View File

@ -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;

14
drivers/target/target_core_transport.c
View File

@ -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;

2
include/target/target_core_base.h
View File

@ -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;