Re: [PATCH v2] EDAC/mc: Fix use-after-free and memleaks during device removal

[John Garry]

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@xxxxxxxxxx>
> 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@xxxxxxxxxxx>
> Acked-by: Aristeu Rozanski <aris@xxxxxxxxxx>
> Signed-off-by: Robert Richter <rrichter@xxxxxxxxxxx>
> ---
> V2:

Kasan warnings and leak reports are gone:
Tested-by: John Garry <john.garry@xxxxxxxxxx>

Cheers