2d9a2c5f58
Before v4.15 commit 75492a51568b ("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: 75492a51568b ("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.