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>

diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
index 0b4b2a6..ae24d0f 100644 (file)
--- a/drivers/target/target_core_sbc.c
+++ b/drivers/target/target_core_sbc.c
@@ -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;

diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 5bacc7b..010b8c4 100644 (file)
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -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;

diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index 0a2c740..aabf0ac 100644 (file)
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -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;