[PATCH v2 9/9] kobject: Require explicit initialization of struct kobj_type::release

[Ian Rogers <irogers@google.com>]

Documentation/core-api/kobject.rst states:

  "One important point cannot be overstated: every kobject must have a
  release() method, and the kobject must persist (in a consistent state)
  until that method is called. If these constraints are not met, the code
  is flawed. Note that the kernel will warn you if you forget to provide
  a release() method. Do not try to get rid of this warning by providing
  an \"empty\" release function."

Annotate struct kobj_type::release with __must_init
so the compiler diagnoses any struct kobj_type initializer that omits
.release.

For the remaining legacy struct kobj_type definitions where the kobject
is static, per-CPU, permanent firmware structures, or embedded inside a
devm- or parent-managed structure rather than freed by kobject_put(),
explicitly initialize .release = NULL with a comment documenting why no
release callback is provided.

Where the existing teardown is not safe with CONFIG_DEBUG_KOBJECT_RELEASE,
because the kobject's memory can be freed or cleared while the delayed
kobject cleanup is still pending (ioat, kunpeng_hccs and omapfb display),
the comment says so. Fixing those is left to follow-up patches; this
change does not alter their behavior.

Link: https://lpc.events/event/20/contributions/2392/
Signed-off-by: Ian Rogers <irogers@google.com>
---
 arch/arm64/kernel/cpuinfo.c                   |  5 +++++
 drivers/acpi/sysfs.c                          |  2 ++
 drivers/dma/ioat/sysfs.c                      |  7 +++++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c    |  5 +++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_xcp.c       | 10 +++++++++
 drivers/infiniband/hw/hfi1/sysfs.c            |  5 +++++
 drivers/infiniband/hw/usnic/usnic_ib_sysfs.c  |  2 ++
 drivers/parisc/pdc_stable.c                   |  5 +++++
 drivers/power/supply/ab8500_fg.c              |  5 +++++
 drivers/s390/char/sclp_mem.c                  |  2 ++
 drivers/soc/hisilicon/kunpeng_hccs.c          | 21 +++++++++++++++++++
 .../fbdev/omap2/omapfb/dss/display-sysfs.c    |  7 +++++++
 .../fbdev/omap2/omapfb/dss/manager-sysfs.c    |  5 +++++
 .../fbdev/omap2/omapfb/dss/overlay-sysfs.c    |  5 +++++
 fs/erofs/sysfs.c                              | 10 +++++++++
 fs/f2fs/sysfs.c                               | 15 +++++++++++++
 fs/ocfs2/cluster/masklog.c                    |  5 +++++
 include/linux/kobject.h                       |  2 +-
 18 files changed, 117 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index 94e6cd211d70..7a4ac8dd0b86 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c
@@ -295,6 +295,11 @@ const struct seq_operations cpuinfo_op = {
 
 
 static const struct kobj_type cpuregs_kobj_type = {
+	/*
+	 * Pre-existing: info->kobj is embedded in per-CPU cpu_data;
+	 * cpuid_cpu_offline() only calls kobject_del().
+	 */
+	.release = NULL,
 	.sysfs_ops = &kobj_sysfs_ops,
 };
 
diff --git a/drivers/acpi/sysfs.c b/drivers/acpi/sysfs.c
index a99373547126..1948b80e8a4a 100644
--- a/drivers/acpi/sysfs.c
+++ b/drivers/acpi/sysfs.c
@@ -973,6 +973,8 @@ static struct attribute *hotplug_profile_attrs[] = {
 ATTRIBUTE_GROUPS(hotplug_profile);
 
 static const struct kobj_type acpi_hotplug_profile_ktype = {
+	/* Pre-existing: hotplug->kobj is embedded in static struct acpi_scan_hotplug objects. */
+	.release = NULL,
 	.sysfs_ops = &kobj_sysfs_ops,
 	.default_groups = hotplug_profile_groups,
 };
diff --git a/drivers/dma/ioat/sysfs.c b/drivers/dma/ioat/sysfs.c
index e796ddb5383f..5ba44876eb96 100644
--- a/drivers/dma/ioat/sysfs.c
+++ b/drivers/dma/ioat/sysfs.c
@@ -167,6 +167,13 @@ static const struct attribute *const ioat_attrs[] = {
 ATTRIBUTE_GROUPS(ioat);
 
 const struct kobj_type ioat_ktype = {
+	/*
+	 * Pre-existing: ioatdma_chan is freed by release_ioatdma(), not
+	 * by kobject_put(). With CONFIG_DEBUG_KOBJECT_RELEASE the delayed
+	 * kobject cleanup queued by ioat_kobject_del() may run after
+	 * that kfree(), a use-after-free.
+	 */
+	.release = NULL,
 	.sysfs_ops = &ioat_sysfs_ops,
 	.default_groups = ioat_groups,
 };
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c
index 17888cf54447..c2cccd924b03 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c
@@ -885,6 +885,11 @@ static const struct attribute_group ualink_xcp_info_group = {
 };
 
 static const struct kobj_type ualink_xcp_info_ktype = {
+	/*
+	 * Pre-existing: xcp->ualink.kobj is embedded in struct amdgpu_xcp_mgr
+	 * rather than freed individually by kobject_put().
+	 */
+	.release = NULL,
 	.sysfs_ops = &kobj_sysfs_ops
 };
 
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_xcp.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_xcp.c
index ab14079d1c42..0847134a1391 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_xcp.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_xcp.c
@@ -797,6 +797,11 @@ static const struct sysfs_ops xcp_cfg_res_sysfs_ops = {
 };
 
 static const struct kobj_type xcp_cfg_res_sysfs_ktype = {
+	/*
+	 * Pre-existing: xcp_res is embedded in struct amdgpu_xcp_cfg
+	 * rather than freed individually by kobject_put().
+	 */
+	.release = NULL,
 	.sysfs_ops = &xcp_cfg_res_sysfs_ops,
 	.default_groups = xcp_cfg_res_sysfs_groups,
 };
@@ -1061,6 +1066,11 @@ static const struct attribute_group amdgpu_xcp_attrs_group = {
 };
 
 static const struct kobj_type xcp_sysfs_ktype = {
+	/*
+	 * Pre-existing: xcp is embedded in struct amdgpu_xcp_mgr
+	 * rather than freed individually by kobject_put().
+	 */
+	.release = NULL,
 	.sysfs_ops = &kobj_sysfs_ops,
 };
 
diff --git a/drivers/infiniband/hw/hfi1/sysfs.c b/drivers/infiniband/hw/hfi1/sysfs.c
index 372cfd13dc61..5a1aca06b542 100644
--- a/drivers/infiniband/hw/hfi1/sysfs.c
+++ b/drivers/infiniband/hw/hfi1/sysfs.c
@@ -608,6 +608,11 @@ static const struct sysfs_ops sde_sysfs_ops = {
 };
 
 static struct kobj_type sde_ktype = {
+	/*
+	 * Pre-existing: sdma_engine is embedded in dd->per_sdma array
+	 * rather than freed by kobject_put().
+	 */
+	.release = NULL,
 	.sysfs_ops = &sde_sysfs_ops,
 };
 
diff --git a/drivers/infiniband/hw/usnic/usnic_ib_sysfs.c b/drivers/infiniband/hw/usnic/usnic_ib_sysfs.c
index fdb63a8fb997..df0e48070c2e 100644
--- a/drivers/infiniband/hw/usnic/usnic_ib_sysfs.c
+++ b/drivers/infiniband/hw/usnic/usnic_ib_sysfs.c
@@ -245,6 +245,8 @@ static struct attribute *usnic_ib_qpn_default_attrs[] = {
 ATTRIBUTE_GROUPS(usnic_ib_qpn_default);
 
 static struct kobj_type usnic_ib_qpn_type = {
+	/* Pre-existing: usnic_ib_qp_grp is embedded in RDMA core-managed struct usnic_ib_qp_grp. */
+	.release = NULL,
 	.sysfs_ops = &usnic_ib_qpn_sysfs_ops,
 	.default_groups = usnic_ib_qpn_default_groups,
 };
diff --git a/drivers/parisc/pdc_stable.c b/drivers/parisc/pdc_stable.c
index 6b567a74fc2c..2f530e8c6757 100644
--- a/drivers/parisc/pdc_stable.c
+++ b/drivers/parisc/pdc_stable.c
@@ -484,6 +484,11 @@ ATTRIBUTE_GROUPS(paths_subsys);
 
 /* Specific kobject type for our PDC paths */
 static const struct kobj_type ktype_pdcspath = {
+	/*
+	 * Pre-existing: pdcspath_entry instances are static; lifetime
+	 * is not controlled by kobject_put().
+	 */
+	.release = NULL,
 	.sysfs_ops = &pdcspath_attr_ops,
 	.default_groups = paths_subsys_groups,
 };
diff --git a/drivers/power/supply/ab8500_fg.c b/drivers/power/supply/ab8500_fg.c
index e6b5efdf5dc9..d62411e4f535 100644
--- a/drivers/power/supply/ab8500_fg.c
+++ b/drivers/power/supply/ab8500_fg.c
@@ -2531,6 +2531,11 @@ static struct attribute *ab8500_fg_attrs[] = {
 ATTRIBUTE_GROUPS(ab8500_fg);
 
 static const struct kobj_type ab8500_fg_ktype = {
+	/*
+	 * Pre-existing: fg_kobject is embedded in devm-allocated struct
+	 * ab8500_fg; ab8500_fg_sysfs_exit() only calls kobject_del().
+	 */
+	.release = NULL,
 	.sysfs_ops = &ab8500_fg_sysfs_ops,
 	.default_groups = ab8500_fg_groups,
 };
diff --git a/drivers/s390/char/sclp_mem.c b/drivers/s390/char/sclp_mem.c
index 6df1926d4c62..2fb7271dce36 100644
--- a/drivers/s390/char/sclp_mem.c
+++ b/drivers/s390/char/sclp_mem.c
@@ -305,6 +305,8 @@ static ssize_t sclp_memmap_on_memory_store(struct kobject *kobj, struct kobj_att
 }
 
 static const struct kobj_type ktype = {
+	/* Pre-existing: permanent firmware kobjects, never freed */
+	.release = NULL,
 	.sysfs_ops = &kobj_sysfs_ops,
 };
 
diff --git a/drivers/soc/hisilicon/kunpeng_hccs.c b/drivers/soc/hisilicon/kunpeng_hccs.c
index 0cc2953d59a5..da7a64c95058 100644
--- a/drivers/soc/hisilicon/kunpeng_hccs.c
+++ b/drivers/soc/hisilicon/kunpeng_hccs.c
@@ -1038,6 +1038,13 @@ static struct attribute *hccs_port_default_attrs[] = {
 ATTRIBUTE_GROUPS(hccs_port_default);
 
 static const struct kobj_type hccs_port_type = {
+	/*
+	 * Pre-existing: hccs_port_info is allocated via devm_kzalloc()
+	 * rather than freed by kobject_put(). With
+	 * CONFIG_DEBUG_KOBJECT_RELEASE the delayed kobject cleanup may run
+	 * after devm frees it on unbind, a use-after-free.
+	 */
+	.release = NULL,
 	.sysfs_ops = &hccs_comm_ops,
 	.default_groups = hccs_port_default_groups,
 };
@@ -1110,6 +1117,13 @@ static struct attribute *hccs_die_default_attrs[] = {
 ATTRIBUTE_GROUPS(hccs_die_default);
 
 static const struct kobj_type hccs_die_type = {
+	/*
+	 * Pre-existing: hccs_die_info is allocated via devm_kzalloc()
+	 * rather than freed by kobject_put(). With
+	 * CONFIG_DEBUG_KOBJECT_RELEASE the delayed kobject cleanup may run
+	 * after devm frees it on unbind, a use-after-free.
+	 */
+	.release = NULL,
 	.sysfs_ops = &hccs_comm_ops,
 	.default_groups = hccs_die_default_groups,
 };
@@ -1213,6 +1227,13 @@ static struct attribute *hccs_chip_default_attrs[] = {
 ATTRIBUTE_GROUPS(hccs_chip_default);
 
 static const struct kobj_type hccs_chip_type = {
+	/*
+	 * Pre-existing: hccs_chip_info is allocated via devm_kzalloc()
+	 * rather than freed by kobject_put(). With
+	 * CONFIG_DEBUG_KOBJECT_RELEASE the delayed kobject cleanup may run
+	 * after devm frees it on unbind, a use-after-free.
+	 */
+	.release = NULL,
 	.sysfs_ops = &hccs_comm_ops,
 	.default_groups = hccs_chip_default_groups,
 };
diff --git a/drivers/video/fbdev/omap2/omapfb/dss/display-sysfs.c b/drivers/video/fbdev/omap2/omapfb/dss/display-sysfs.c
index ae937854403b..452920a4e2a9 100644
--- a/drivers/video/fbdev/omap2/omapfb/dss/display-sysfs.c
+++ b/drivers/video/fbdev/omap2/omapfb/dss/display-sysfs.c
@@ -304,6 +304,13 @@ static const struct sysfs_ops display_sysfs_ops = {
 };
 
 static struct kobj_type display_ktype = {
+	/*
+	 * Pre-existing: dssdev->kobj is embedded in struct omap_dss_device
+	 * and zeroed in display_uninit_sysfs() right after kobject_put().
+	 * With CONFIG_DEBUG_KOBJECT_RELEASE that memset() clobbers the
+	 * pending delayed kobject cleanup.
+	 */
+	.release = NULL,
 	.sysfs_ops = &display_sysfs_ops,
 	.default_groups = display_sysfs_groups,
 };
diff --git a/drivers/video/fbdev/omap2/omapfb/dss/manager-sysfs.c b/drivers/video/fbdev/omap2/omapfb/dss/manager-sysfs.c
index 1b644be5fe2e..40ec750f4315 100644
--- a/drivers/video/fbdev/omap2/omapfb/dss/manager-sysfs.c
+++ b/drivers/video/fbdev/omap2/omapfb/dss/manager-sysfs.c
@@ -496,6 +496,11 @@ static const struct sysfs_ops manager_sysfs_ops = {
 };
 
 static struct kobj_type manager_ktype = {
+	/*
+	 * Pre-existing: mgr->kobj is embedded in static managers[] and
+	 * zeroed in dss_manager_kobj_uninit().
+	 */
+	.release = NULL,
 	.sysfs_ops = &manager_sysfs_ops,
 	.default_groups = manager_sysfs_groups,
 };
diff --git a/drivers/video/fbdev/omap2/omapfb/dss/overlay-sysfs.c b/drivers/video/fbdev/omap2/omapfb/dss/overlay-sysfs.c
index 1da4fb1c77b4..4d333031b18d 100644
--- a/drivers/video/fbdev/omap2/omapfb/dss/overlay-sysfs.c
+++ b/drivers/video/fbdev/omap2/omapfb/dss/overlay-sysfs.c
@@ -429,6 +429,11 @@ static const struct sysfs_ops overlay_sysfs_ops = {
 };
 
 static struct kobj_type overlay_ktype = {
+	/*
+	 * Pre-existing: ovl->kobj is embedded in static overlays[];
+	 * dss_overlay_kobj_uninit() drops the kobject ref.
+	 */
+	.release = NULL,
 	.sysfs_ops = &overlay_sysfs_ops,
 	.default_groups = overlay_sysfs_groups,
 };
diff --git a/fs/erofs/sysfs.c b/fs/erofs/sysfs.c
index dfcec9376cd5..2ea6773cd98f 100644
--- a/fs/erofs/sysfs.c
+++ b/fs/erofs/sysfs.c
@@ -238,6 +238,11 @@ static const struct kobj_type erofs_sb_ktype = {
 static const struct kobj_type erofs_ktype = {
 	.default_groups = erofs_groups,
 	.sysfs_ops	= &erofs_attr_ops,
+	/*
+	 * Pre-existing: erofs_root is a static struct kset; lifetime
+	 * is not controlled by kobject_put().
+	 */
+	.release	= NULL,
 };
 
 static struct kset erofs_root = {
@@ -247,6 +252,11 @@ static struct kset erofs_root = {
 static const struct kobj_type erofs_feat_ktype = {
 	.default_groups = erofs_feat_groups,
 	.sysfs_ops	= &erofs_attr_ops,
+	/*
+	 * Pre-existing: erofs_feat is a static struct kobject; lifetime
+	 * is not controlled by kobject_put().
+	 */
+	.release	= NULL,
 };
 
 static struct kobject erofs_feat = {
diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index 430356e500af..6e15695cb75f 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -1683,6 +1683,11 @@ static const struct kobj_type f2fs_sb_ktype = {
 
 static const struct kobj_type f2fs_ktype = {
 	.sysfs_ops	= &f2fs_attr_ops,
+	/*
+	 * Pre-existing: f2fs_kset is a static struct kset; lifetime
+	 * is not controlled by kobject_put().
+	 */
+	.release	= NULL,
 };
 
 static struct kset f2fs_kset = {
@@ -1697,6 +1702,11 @@ static const struct sysfs_ops f2fs_feat_attr_ops = {
 static const struct kobj_type f2fs_feat_ktype = {
 	.default_groups = f2fs_feat_groups,
 	.sysfs_ops	= &f2fs_feat_attr_ops,
+	/*
+	 * Pre-existing: f2fs_feat is a static struct kobject; lifetime
+	 * is not controlled by kobject_put().
+	 */
+	.release	= NULL,
 };
 
 static struct kobject f2fs_feat = {
@@ -1711,6 +1721,11 @@ static const struct sysfs_ops f2fs_tune_attr_ops = {
 static const struct kobj_type f2fs_tune_ktype = {
 	.default_groups = f2fs_tune_groups,
 	.sysfs_ops	= &f2fs_tune_attr_ops,
+	/*
+	 * Pre-existing: f2fs_tune is a static struct kobject; lifetime
+	 * is not controlled by kobject_put().
+	 */
+	.release	= NULL,
 };
 
 static struct kobject f2fs_tune = {
diff --git a/fs/ocfs2/cluster/masklog.c b/fs/ocfs2/cluster/masklog.c
index 563881ddbf00..ff8a1cf51e72 100644
--- a/fs/ocfs2/cluster/masklog.c
+++ b/fs/ocfs2/cluster/masklog.c
@@ -147,6 +147,11 @@ static const struct sysfs_ops mlog_attr_ops = {
 static struct kobj_type mlog_ktype = {
 	.default_groups = mlog_default_groups,
 	.sysfs_ops      = &mlog_attr_ops,
+	/*
+	 * Pre-existing: mlog_kset is a static struct kset; lifetime
+	 * is not controlled by kobject_put().
+	 */
+	.release        = NULL,
 };
 
 static struct kset mlog_kset = {
diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index 55e37a5d405e..8a1332030884 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -114,7 +114,7 @@ void kobject_get_ownership(const struct kobject *kobj, kuid_t *uid, kgid_t *gid)
 char *kobject_get_path(const struct kobject *kobj, gfp_t flag);
 
 struct kobj_type {
-	void (*release)(struct kobject *kobj);
+	void (*release)(struct kobject *kobj) __must_init;
 	const struct sysfs_ops *sysfs_ops;
 	const struct attribute_group **default_groups;
 	const struct kobj_ns_type_operations *(*child_ns_type)(const struct kobject *kobj);
-- 
2.56.0.313.g2479322e68-goog