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Steffen Maier
2d9a2c5f58
Before v4.15 commit75492a5156("s390/scsi: Convert timers to use timer_setup()"), we intentionally only passed zfcp_adapter as context argument to zfcp_fsf_request_timeout_handler(). Since we only trigger adapter recovery, it was unnecessary to sync against races between timeout and (late) completion. Likewise, we only passed zfcp_erp_action as context argument to zfcp_erp_timeout_handler(). Since we only wakeup an ERP action, it was unnecessary to sync against races between timeout and (late) completion. Meanwhile the timeout handlers get timer_list as context argument and do a timer-specific container-of to zfcp_fsf_req which can have been freed. Fix it by making sure that any request timeout handlers, that might just have started before del_timer(), are completed by using del_timer_sync() instead. This ensures the request free happens afterwards. Space time diagram of potential use-after-free: Basic idea is to have 2 or more pending requests whose timeouts run out at almost the same time. req 1 timeout ERP thread req 2 timeout ---------------- ---------------- --------------------------------------- zfcp_fsf_request_timeout_handler fsf_req = from_timer(fsf_req, t, timer) adapter = fsf_req->adapter zfcp_qdio_siosl(adapter) zfcp_erp_adapter_reopen(adapter,...) zfcp_erp_strategy ... zfcp_fsf_req_dismiss_all list_for_each_entry_safe zfcp_fsf_req_complete 1 del_timer 1 zfcp_fsf_req_free 1 zfcp_fsf_req_complete 2 zfcp_fsf_request_timeout_handler del_timer 2 fsf_req = from_timer(fsf_req, t, timer) zfcp_fsf_req_free 2 adapter = fsf_req->adapter ^^^^^^^ already freed Link: https://lore.kernel.org/r/20200813152856.50088-1-maier@linux.ibm.com Fixes:75492a5156("s390/scsi: Convert timers to use timer_setup()") Cc: <stable@vger.kernel.org> #4.15+ Suggested-by: Julian Wiedmann <jwi@linux.ibm.com> Reviewed-by: Julian Wiedmann <jwi@linux.ibm.com> Signed-off-by: Steffen Maier <maier@linux.ibm.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.