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Tue, 03 Nov 2026 06:40:16 -0800 (PST) Received: from localhost.localdomain ([2400:d802:dd7:8000:314f:4575:be3:a064]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2eb39052edasm42898465ad.4.2026.11.03.06.40.13 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Tue, 03 Nov 2026 06:40:16 -0800 (PST) From: Yuqiang Sun To: haiyangz@microsoft.com, wei.liu@kernel.org, decui@microsoft.com Cc: mhklinux@outlook.com, stephen@networkplumber.org, linmq006@gmail.com, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH v3 1/2] Drivers: hv: vmbus: Keep the channel when vmbus_add_channel_kobj() fails Date: Tue, 3 Nov 2026 22:40:05 +0800 Message-ID: <20261103144006.69857-2-izaiahsun@gmail.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20261103144006.69857-1-izaiahsun@gmail.com> References: <20261103144006.69857-1-izaiahsun@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The channel is freed by the release of its kobject, and free_channel() drops that reference. Since commit 8bc69f86328e ("Drivers: hv: vmbus: Fix memory leak in vmbus_add_channel_kobj"), vmbus_add_channel_kobj() also drops it when it fails, as kobject_init_and_add() asks for. That frees the channel, and both callers then go on with it: vmbus_add_channel_work() unlinks a sub-channel, unmaps and releases its relid and calls free_channel(), a use after free and a second kobject_put(); for a primary channel, vmbus_device_register() unwinds through vmbus_device_release(), which removes the channel too. The kobject is also only initialized in vmbus_add_channel_kobj(), so the error paths before it, for instance a vmbus_device_create() failure in vmbus_add_channel_work(), call free_channel() on a kobject that was never initialized: kobject_put() warns and does nothing, so the channel is leaked, and removing the attribute group from a kobject that is not in sysfs warns as well. Initialize the kobject when the channel is allocated, so that free_channel() is the one place that drops its reference on every path. vmbus_add_channel_kobj() then only adds it, and leaves the reference to its callers when it fails. Remove the attribute group only if the kobject was added. Fixes: c2e5df616e1a ("vmbus: add per-channel sysfs info") Fixes: 8bc69f86328e ("Drivers: hv: vmbus: Fix memory leak in vmbus_add_channel_kobj") Cc: stable@vger.kernel.org Signed-off-by: Yuqiang Sun --- Notes: The bug was found with kbound, a research static analysis prototype. The patch, the changelog and the test setup were written with the help of an AI coding assistant (Claude); I have reviewed them and tested them as described in the cover letter. drivers/hv/channel_mgmt.c | 5 +++-- drivers/hv/hyperv_vmbus.h | 1 + drivers/hv/vmbus_drv.c | 25 ++++++++++++++++++------- 3 files changed, 22 insertions(+), 9 deletions(-) diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c index c42def04ac41..cb1d8d76928f 100644 --- a/drivers/hv/channel_mgmt.c +++ b/drivers/hv/channel_mgmt.c @@ -367,6 +367,7 @@ static struct vmbus_channel *alloc_channel(void) vmbus_on_event, (unsigned long)channel); hv_ringbuffer_pre_init(channel); + vmbus_init_channel_kobj(channel); return channel; } @@ -663,8 +664,8 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel) mutex_unlock(&vmbus_connection.channel_mutex); cpus_read_unlock(); /* - * Don't call free_channel(), because newchannel->kobj - * is not initialized yet. + * Don't call free_channel(): newchannel was never + * added, and its kobject holds nothing yet. */ kfree(newchannel); WARN_ON_ONCE(1); diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h index 33923621a5a3..7865a519dd7f 100644 --- a/drivers/hv/hyperv_vmbus.h +++ b/drivers/hv/hyperv_vmbus.h @@ -408,6 +408,7 @@ struct hv_device *vmbus_device_create(const guid_t *type, int vmbus_device_register(struct hv_device *child_device_obj); void vmbus_device_unregister(struct hv_device *device_obj); +void vmbus_init_channel_kobj(struct vmbus_channel *channel); int vmbus_add_channel_kobj(struct hv_device *device_obj, struct vmbus_channel *channel); diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c index 4692687cdbf3..fc0f16f51266 100644 --- a/drivers/hv/vmbus_drv.c +++ b/drivers/hv/vmbus_drv.c @@ -2084,6 +2084,15 @@ int hv_remove_ring_sysfs(struct vmbus_channel *channel) } EXPORT_SYMBOL_GPL(hv_remove_ring_sysfs); +/* + * vmbus_init_channel_kobj - initialize the kobject that holds the channel's + * lifetime; free_channel() drops its reference + */ +void vmbus_init_channel_kobj(struct vmbus_channel *channel) +{ + kobject_init(&channel->kobj, &vmbus_chan_ktype); +} + /* * vmbus_add_channel_kobj - setup a sub-directory under device/channels */ @@ -2094,13 +2103,14 @@ int vmbus_add_channel_kobj(struct hv_device *dev, struct vmbus_channel *channel) u32 relid = channel->offermsg.child_relid; int ret; + /* + * On failure the kobject keeps its reference: the callers' error + * paths drop it in free_channel(), which also frees the channel. + */ kobj->kset = dev->channels_kset; - ret = kobject_init_and_add(kobj, &vmbus_chan_ktype, NULL, - "%u", relid); - if (ret) { - kobject_put(kobj); + ret = kobject_add(kobj, NULL, "%u", relid); + if (ret) return ret; - } ret = sysfs_create_group(kobj, &vmbus_chan_group); @@ -2109,7 +2119,6 @@ int vmbus_add_channel_kobj(struct hv_device *dev, struct vmbus_channel *channel) * The calling functions' error handling paths will cleanup the * empty channel directory. */ - kobject_put(kobj); dev_err(device, "Unable to set up channel sysfs files\n"); return ret; } @@ -2124,7 +2133,9 @@ int vmbus_add_channel_kobj(struct hv_device *dev, struct vmbus_channel *channel) */ void vmbus_remove_channel_attr_group(struct vmbus_channel *channel) { - sysfs_remove_group(&channel->kobj, &vmbus_chan_group); + /* A channel that failed before vmbus_add_channel_kobj() has none */ + if (channel->kobj.state_in_sysfs) + sysfs_remove_group(&channel->kobj, &vmbus_chan_group); } /* -- 2.53.0