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Date: Thu, 29 Feb 2024 23:31:17 +0100
From: Greg Kroah-Hartman <>
Cc: Greg Kroah-Hartman <>
Subject: CVE-2021-46959: spi: Fix use-after-free with devm_spi_alloc_*


In the Linux kernel, the following vulnerability has been resolved:

spi: Fix use-after-free with devm_spi_alloc_*

We can't rely on the contents of the devres list during
spi_unregister_controller(), as the list is already torn down at the
time we perform devres_find() for devm_spi_release_controller. This
causes devices registered with devm_spi_alloc_{master,slave}() to be
mistakenly identified as legacy, non-devm managed devices and have their
reference counters decremented below 0.

------------[ cut here ]------------
WARNING: CPU: 1 PID: 660 at lib/refcount.c:28 refcount_warn_saturate+0x108/0x174
[<b0396f04>] (refcount_warn_saturate) from [<b03c56a4>] (kobject_put+0x90/0x98)
[<b03c5614>] (kobject_put) from [<b0447b4c>] (put_device+0x20/0x24)
[<b0447b2c>] (put_device) from [<b07515e8>] (devm_spi_release_controller+0x3c/0x40)
[<b07515ac>] (devm_spi_release_controller) from [<b045343c>] (release_nodes+0x84/0xc4)
 r5:b6700180 r4:b6700100
[<b04533b8>] (release_nodes) from [<b0454160>] (devres_release_all+0x5c/0x60)
 r8:b1638c54 r7:b117ad94 r6:b1638c10 r5:b117ad94 r4:b163dc10
[<b0454104>] (devres_release_all) from [<b044e41c>] (__device_release_driver+0x144/0x1ec)
 r5:b117ad94 r4:b163dc10
[<b044e2d8>] (__device_release_driver) from [<b044f70c>] (device_driver_detach+0x84/0xa0)
 r9:00000000 r8:00000000 r7:b117ad94 r6:b163dc54 r5:b1638c10 r4:b163dc10
[<b044f688>] (device_driver_detach) from [<b044d274>] (unbind_store+0xe4/0xf8)

Instead, determine the devm allocation state as a flag on the
controller which is guaranteed to be stable during cleanup.

The Linux kernel CVE team has assigned CVE-2021-46959 to this issue.

Affected and fixed versions

	Issue introduced in 4.4.248 with commit 0713aa02f20d and fixed in 4.4.271 with commit 62bb2c7f2411
	Issue introduced in 4.9.248 with commit 2be1837b1737 and fixed in 4.9.271 with commit 8bf96425c90f
	Issue introduced in 4.14.212 with commit e620a73d7ca7 and fixed in 4.14.233 with commit 8e029707f50a
	Issue introduced in 4.19.163 with commit c886774bf583 and fixed in 4.19.191 with commit 28a5529068c5
	Issue introduced in 5.4.80 with commit 2737549129ec and fixed in 5.4.119 with commit 001c8e83646a
	Issue introduced in 5.10 with commit 5e844cc37a5c and fixed in 5.10.37 with commit c7fabe372a90
	Issue introduced in 5.10 with commit 5e844cc37a5c and fixed in 5.11.21 with commit cee78aa24578
	Issue introduced in 5.10 with commit 5e844cc37a5c and fixed in 5.12.4 with commit 8735248ebb91
	Issue introduced in 5.10 with commit 5e844cc37a5c and fixed in 5.13 with commit 794aaf01444d

Please see or a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files

The file(s) affected by this issue are:


The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:

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