[PATCH] vduse: Fix NULL pointer dereference on sysfs access

From: Xie Yongji <xieyongji@bytedance.com>
To: mst@redhat.com, jasowang@redhat.com
Cc: mcgrof@kernel.org, akpm@linux-foundation.org,
	oliver.sang@intel.com, virtualization@lists.linux-foundation.org,
	stable@vger.kernel.org
Subject: [PATCH] vduse: Fix NULL pointer dereference on sysfs access
Date: Tue, 26 Apr 2022 14:01:03 +0800	[thread overview]
Message-ID: <20220426060103.104-1-xieyongji@bytedance.com> (raw)

The control device has no drvdata. So we will get a NULL
NULL pointer dereference when accessing control device's
msg_timeout via sysfs:

[ 132.841881][ T3644] BUG: kernel NULL pointer dereference, address: 00000000000000f8
[ 132.850619][ T3644] RIP: 0010:msg_timeout_show (drivers/vdpa/vdpa_user/vduse_dev.c:1271)
[ 132.869447][ T3644] dev_attr_show (drivers/base/core.c:2094)
[ 132.870215][ T3644] sysfs_kf_seq_show (fs/sysfs/file.c:59)
[ 132.871164][ T3644] ? device_remove_bin_file (drivers/base/core.c:2088)
[ 132.872082][ T3644] kernfs_seq_show (fs/kernfs/file.c:164)
[ 132.872838][ T3644] seq_read_iter (fs/seq_file.c:230)
[ 132.873578][ T3644] ? __vmalloc_area_node (mm/vmalloc.c:3041)
[ 132.874532][ T3644] kernfs_fop_read_iter (fs/kernfs/file.c:238)
[ 132.875513][ T3644] __kernel_read (fs/read_write.c:440 (discriminator 1))
[ 132.876319][ T3644] kernel_read (fs/read_write.c:459)
[ 132.877129][ T3644] kernel_read_file (fs/kernel_read_file.c:94)
[ 132.877978][ T3644] kernel_read_file_from_fd (include/linux/file.h:45 fs/kernel_read_file.c:186)
[ 132.879019][ T3644] __do_sys_finit_module (kernel/module.c:4207)
[ 132.879930][ T3644] __ia32_sys_finit_module (kernel/module.c:4189)
[ 132.880930][ T3644] do_int80_syscall_32 (arch/x86/entry/common.c:112 arch/x86/entry/common.c:132)
[ 132.881847][ T3644] entry_INT80_compat (arch/x86/entry/entry_64_compat.S:419)

To fix it, let's add a NULL check in msg_timeout_show() and
msg_timeout_store().

Fixes: c8a6153b6c59 ("vduse: Introduce VDUSE - vDPA Device in Userspace")
Reported-by: kernel test robot <oliver.sang@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
---
 drivers/vdpa/vdpa_user/vduse_dev.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
index f85d1a08ed87..f1c42f4aabb4 100644
--- a/drivers/vdpa/vdpa_user/vduse_dev.c
+++ b/drivers/vdpa/vdpa_user/vduse_dev.c
@@ -1268,6 +1268,9 @@ static ssize_t msg_timeout_show(struct device *device,
 {
 	struct vduse_dev *dev = dev_get_drvdata(device);
 
+	if (!dev)
+		return -EPERM;
+
 	return sysfs_emit(buf, "%u\n", dev->msg_timeout);
 }
 
@@ -1278,6 +1281,9 @@ static ssize_t msg_timeout_store(struct device *device,
 	struct vduse_dev *dev = dev_get_drvdata(device);
 	int ret;
 
+	if (!dev)
+		return -EPERM;
+
 	ret = kstrtouint(buf, 10, &dev->msg_timeout);
 	if (ret < 0)
 		return ret;
-- 
2.20.1

