Loading
target: Check sess_tearing_down in target_get_sess_cmd()
Target core code assumes that target_splice_sess_cmd_list() has set sess_tearing_down and moved the list of pending commands to sess_wait_list, no more commands will be added to the session; if any are added, nothing keeps the se_session from being freed while the command is still in flight, which e.g. leads to use-after-free of se_cmd->se_sess in target_release_cmd_kref(). To enforce this invariant, put a check of sess_tearing_down inside of sess_cmd_lock in target_get_sess_cmd(); any checks before this are racy and can lead to the use-after-free described above. For example, the qla_target check in qlt_do_work() checks sess_tearing_down from work thread context but then drops all locks before calling target_submit_cmd() (as it must, since that is a sleeping function). However, since no locks are held, anything can happen with respect to the session it has looked up -- although it does correctly get sess_kref within its lock, so the memory won't be freed while target_submit_cmd() is actually running, nothing stops eg an ACL from being dropped and calling ->shutdown_session() (which calls into target_splice_sess_cmd_list()) before we get to target_get_sess_cmd(). Once this happens, the se_session memory can be freed as soon as target_submit_cmd() returns and qlt_do_work() drops its reference, even though we've just added a command to sess_cmd_list. To prevent this use-after-free, check sess_tearing_down inside of sess_cmd_lock right before target_get_sess_cmd() adds a command to sess_cmd_list; this is synchronized with target_splice_sess_cmd_list() so that every command is either waited for or not added to the queue. (nab: Keep target_submit_cmd() returning void for now..) Signed-off-by:Roland Dreier <roland@purestorage.com> Signed-off-by: