[PATCH AUTOSEL 5.2 30/76] scsi: target: tcmu: avoid use-after-free after command timeout

Sasha Levin
2019-08-29T18:32:21Z

From: Dmitry Fomichev <dmitry.fomichev@wdc.com>

[ Upstream commit a86a75865ff4d8c05f355d1750a5250aec89ab15 ]

In tcmu_handle_completion() function, the variable called read_len is
always initialized with a value taken from se_cmd structure. If this
function is called to complete an expired (timed out) out command, the
session command pointed by se_cmd is likely to be already deallocated by
the target core at that moment. As the result, this access triggers a
use-after-free warning from KASAN.

This patch fixes the code not to touch se_cmd when completing timed out
TCMU commands. It also resets the pointer to se_cmd at the time when the
TCMU_CMD_BIT_EXPIRED flag is set because it is going to become invalid
after calling target_complete_cmd() later in the same function,
tcmu_check_expired_cmd().

Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Acked-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/target/target_core_user.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index b43d6385a1a09..95b2371fb67b6 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -1132,14 +1132,16 @@ static void tcmu_handle_completion(struct tcmu_cmd *cmd, struct tcmu_cmd_entry *
struct se_cmd *se_cmd = cmd->se_cmd;
struct tcmu_dev *udev = cmd->tcmu_dev;
bool read_len_valid = false;
- uint32_t read_len = se_cmd->data_length;
+ uint32_t read_len;

/*
* cmd has been completed already from timeout, just reclaim
* data area space and free cmd
*/
- if (test_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags))
+ if (test_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags)) {
+ WARN_ON_ONCE(se_cmd);
goto out;
+ }

list_del_init(&cmd->queue_entry);

@@ -1152,6 +1154,7 @@ static void tcmu_handle_completion(struct tcmu_cmd *cmd, struct tcmu_cmd_entry *
goto done;
}

+ read_len = se_cmd->data_length;
if (se_cmd->data_direction == DMA_FROM_DEVICE &&
(entry->hdr.uflags & TCMU_UFLAG_READ_LEN) && entry->rsp.read_len) {
read_len_valid = true;
@@ -1307,6 +1310,7 @@ static int tcmu_check_expired_cmd(int id, void *p, void *data)
*/
scsi_status = SAM_STAT_CHECK_CONDITION;
list_del_init(&cmd->queue_entry);
+ cmd->se_cmd = NULL;
} else {
list_del_init(&cmd->queue_entry);
idr_remove(&udev->commands, id);
@@ -2024,6 +2028,7 @@ static void tcmu_reset_ring(struct tcmu_dev *udev, u8 err_level)

idr_remove(&udev->commands, i);
if (!test_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags)) {
+ WARN_ON(!cmd->se_cmd);
list_del_init(&cmd->queue_entry);
if (err_level == 1) {
/*
--
2.20.1