Messages in this thread | | | Subject | Re: [PATCH v2] EDAC/mc: Fix use-after-free and memleaks during device removal | From | John Garry <> | Date | Thu, 6 Feb 2020 13:35:15 +0000 |
| |
On 05/02/2020 21:24, Robert Richter wrote: > A test kernel with the options set below revealed several issues when > removing a mci device: > > DEBUG_TEST_DRIVER_REMOVE > KASAN > DEBUG_KMEMLEAK > > Issues seen: > > 1) Use-after-free: > > On 27.11.19 17:07:33, John Garry wrote: >> [ 22.104498] BUG: KASAN: use-after-free in >> edac_remove_sysfs_mci_device+0x148/0x180 > > The use-after-free is caused by the mci_for_each_dimm() iterator that > is called in edac_remove_sysfs_mci_device(). The iterator was > introduced with commit c498afaf7df8 ("EDAC: Introduce an > mci_for_each_dimm() iterator"). The iterator loop calls function > device_unregister(&dimm->dev), which removes the sysfs entry of the > device, but also frees the dimm struct in dimm_attr_release(). When > incrementing the loop in mci_for_each_dimm(), the dimm struct is > accessed again, but it is already freed. > > The fix is to free all the mci device's subsequent dimm and csrow > objects at a later point when the mci device is freed. This keeps the > data structures intact and the mci device can be fully used until its > removal. > > 2) Memory leaks: > > Following memory leaks have been detected: > > # grep edac /sys/kernel/debug/kmemleak | sort | uniq -c > 1 [<000000003c0f58f9>] edac_mc_alloc+0x3bc/0x9d0 # mci->csrows > 16 [<00000000bb932dc0>] edac_mc_alloc+0x49c/0x9d0 # csr->channels > 16 [<00000000e2734dba>] edac_mc_alloc+0x518/0x9d0 # csr->channels[chn] > 1 [<00000000eb040168>] edac_mc_alloc+0x5c8/0x9d0 # mci->dimms > 34 [<00000000ef737c29>] ghes_edac_register+0x1c8/0x3f8 # see edac_mc_alloc() > > All leaks are from memory created by edac_mc_alloc(). > > Note: The test above shows that edac_mc_alloc() was called here from > ghes_edac_register(), thus both functions show up in the stack dump, > but the driver causing the leaks is edac_mc. The comments with the > data structures involved were made manually by analyzing the objdump. > > The data structures listed above and created by edac_mc_alloc() are > not properly removed during device removal, which is done in > edac_mc_free(). There are two paths implemented to remove the device > depending on device registration, _edac_mc_free() is called if the > device is not registered and edac_unregister_sysfs() otherwise. The > implemenations differ. For the sysfs case the mci device removal lacks > the removal of subsequent data structures (csrows, channels, dimms). > This causes the memory leaks (see mci_attr_release()). > > Fixing this as follows: > > Unify code and implement a mci_release() function which is used to > remove a struct mci regardless of the device registration status. Use > put_device() to release the struct. Free all subsequent data structs > of the mci's children in that release function. An effect of this is > that no data is freed in edac_mc_sysfs.c (except the "mc" sysfs root > node). All sysfs entries have the mci device as a parent, so its > refcount will keep the mci parent as long as sysfs entries exist. This > prevents struct mci from being freed until all sysfs entries have been > removed which is done in edac_remove_sysfs_mci_device(). With the > changes made the mci_for_each_dimm() loop is now save to release dimm > devices from sysfs. > > The patch has been tested with the above kernel options, no issues > seen any longer. > > Reported-by: John Garry <john.garry@huawei.com> > Fixes: c498afaf7df8 ("EDAC: Introduce an mci_for_each_dimm() iterator") > Fixes: faa2ad09c01c ("edac_mc: edac_mc_free() cannot assume mem_ctl_info is registered in sysfs.") > Fixes: 7a623c039075 ("edac: rewrite the sysfs code to use struct device") > Signed-off-by: Robert Richter <rrichter@marvell.com> > Acked-by: Aristeu Rozanski <aris@redhat.com> > Signed-off-by: Robert Richter <rrichter@marvell.com> > --- > V2:
Kasan warnings and leak reports are gone: Tested-by: John Garry <john.garry@huawei.com>
Cheers
| |