tjh.dev/kernel at v5.6-rc2

A test kernel with the options DEBUG_TEST_DRIVER_REMOVE, KASAN and
DEBUG_KMEMLEAK set, revealed several issues when removing an mci device:

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() macro called in
edac_remove_sysfs_mci_device(). The iterator was introduced with

c498afaf7df8 ("EDAC: Introduce an mci_for_each_dimm() iterator").

The iterator loop calls 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, after having been freed already.

The fix is to free all the mci device's subsequent dimm and csrow
objects at a later point, in _edac_mc_free(), when the mci device itself
is being freed.

This keeps the data structures intact and the mci device can be
fully used until its removal. The change allows the safe usage of
mci_for_each_dimm() to release dimm devices from sysfs.

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 allocated 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 trace
but the module 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()).

[ bp: Massage commit message. ]

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")
Reported-by: John Garry <john.garry@huawei.com>
Signed-off-by: Robert Richter <rrichter@marvell.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: John Garry <john.garry@huawei.com>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20200212120340.4764-3-rrichter@marvell.com

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README

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.

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