[PATCH 4.9 107/116] target/user: Fix use-after-free of tcmu_cmds if they are expired

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andy Grover <agrover@xxxxxxxxxx>

commit d0905ca757bc40bd1ebc261a448a521b064777d7 upstream.

Don't free the cmd in tcmu_check_expired_cmd, it's still referenced by
an entry in our cmd_id->cmd idr. If userspace ever resumes processing,
tcmu_handle_completions() will use the now-invalid cmd pointer.

Instead, don't free cmd. It will be freed by tcmu_handle_completion() if
userspace ever recovers, or tcmu_free_device if not.

Reported-by: Bryant G Ly <bgly@xxxxxxxxxx>
Tested-by: Bryant G Ly <bgly@xxxxxxxxxx>
Signed-off-by: Andy Grover <agrover@xxxxxxxxxx>
Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/target/target_core_user.c |    2 --
 1 file changed, 2 deletions(-)

--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -685,8 +685,6 @@ static int tcmu_check_expired_cmd(int id
 	target_complete_cmd(cmd->se_cmd, SAM_STAT_CHECK_CONDITION);
 	cmd->se_cmd = NULL;
 
-	kmem_cache_free(tcmu_cmd_cache, cmd);
-
 	return 0;
 }