linux-kernel - [PATCH AUTOSEL 5.4 192/266] scsi: target: tcmu: Fix a use after free in tcmu_check_expired_queue

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Date:   Wed, 17 Jun 2020 21:15:17 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        Mike Christie <mchristi@...hat.com>,
        David Disseldorp <ddiss@...e.de>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Sasha Levin <sashal@...nel.org>, linux-scsi@...r.kernel.org,
        target-devel@...r.kernel.org
Subject: [PATCH AUTOSEL 5.4 192/266] scsi: target: tcmu: Fix a use after free in tcmu_check_expired_queue_cmd()

From: Dan Carpenter <dan.carpenter@...cle.com>

[ Upstream commit 9d7464b18892332e35ff37f0b024429a1a9835e6 ]

The pr_debug() dereferences "cmd" after we already freed it by calling
tcmu_free_cmd(cmd).  The debug printk needs to be done earlier.

Link: https://lore.kernel.org/r/20200523101129.GB98132@mwanda
Fixes: 61fb24822166 ("scsi: target: tcmu: Userspace must not complete queued commands")
Reviewed-by: Mike Christie <mchristi@...hat.com>
Reviewed-by: David Disseldorp <ddiss@...e.de>
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/target/target_core_user.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index 70c64e69a1d2..a497e7c1f4fc 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -1292,13 +1292,13 @@ static void tcmu_check_expired_queue_cmd(struct tcmu_cmd *cmd)
 	if (!time_after(jiffies, cmd->deadline))
 		return;
 
+	pr_debug("Timing out queued cmd %p on dev %s.\n",
+		  cmd, cmd->tcmu_dev->name);
+
 	list_del_init(&cmd->queue_entry);
 	se_cmd = cmd->se_cmd;
 	tcmu_free_cmd(cmd);
 
-	pr_debug("Timing out queued cmd %p on dev %s.\n",
-		  cmd, cmd->tcmu_dev->name);
-
 	target_complete_cmd(se_cmd, SAM_STAT_TASK_SET_FULL);
 }
 
-- 
2.25.1