From: yangshiguang yangshiguang@xiaomi.com
Check in debugfs_read_file_str() if the string pointer is NULL.
When creating a node using debugfs_create_str(), the string parameter value can be NULL to indicate empty/unused/ignored. However, reading this node using debugfs_read_file_str() will cause a kernel panic. This should not be fatal, so return an invalid error.
Signed-off-by: yangshiguang yangshiguang@xiaomi.com Fixes: 9af0440ec86e ("debugfs: Implement debugfs_create_str()") Cc: stable@vger.kernel.org --- fs/debugfs/file.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c index 3ec3324c2060..a22ff0ceb230 100644 --- a/fs/debugfs/file.c +++ b/fs/debugfs/file.c @@ -1026,6 +1026,9 @@ ssize_t debugfs_read_file_str(struct file *file, char __user *user_buf, return ret;
str = *(char **)file->private_data; + if (!str) + return -EINVAL; + len = strlen(str) + 1; copy = kmalloc(len, GFP_KERNEL); if (!copy) {
On Mon, Dec 22, 2025 at 05:36:16PM +0800, yangshiguang1011@163.com wrote:
From: yangshiguang yangshiguang@xiaomi.com
Check in debugfs_read_file_str() if the string pointer is NULL.
When creating a node using debugfs_create_str(), the string parameter value can be NULL to indicate empty/unused/ignored.
Why would you create an empty debugfs string file? That is not ok, we should change that to not allow this.
However, reading this node using debugfs_read_file_str() will cause a kernel panic. This should not be fatal, so return an invalid error.
Signed-off-by: yangshiguang yangshiguang@xiaomi.com Fixes: 9af0440ec86e ("debugfs: Implement debugfs_create_str()") Cc: stable@vger.kernel.org
fs/debugfs/file.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c index 3ec3324c2060..a22ff0ceb230 100644 --- a/fs/debugfs/file.c +++ b/fs/debugfs/file.c @@ -1026,6 +1026,9 @@ ssize_t debugfs_read_file_str(struct file *file, char __user *user_buf, return ret; str = *(char **)file->private_data;
- if (!str)
return -EINVAL;
What in kernel user causes this to happen? Let's fix that up instead please.
thanks,
greg k-h
At 2025-12-22 19:54:22, "Greg KH" gregkh@linuxfoundation.org wrote:
On Mon, Dec 22, 2025 at 05:36:16PM +0800, yangshiguang1011@163.com wrote:
From: yangshiguang yangshiguang@xiaomi.com
Check in debugfs_read_file_str() if the string pointer is NULL.
When creating a node using debugfs_create_str(), the string parameter value can be NULL to indicate empty/unused/ignored.
Why would you create an empty debugfs string file? That is not ok, we should change that to not allow this.
Hi greg k-h,
Thanks for your reply.
This is due to the usage step, should write first and then read. However, there is no way to guarantee that everyone will know about this step.
And debugfs_create_str() allows passing in a NULL string. Therefore, when reading a NULL string, should return an invalid error instead of panic.
However, reading this node using debugfs_read_file_str() will cause a kernel panic. This should not be fatal, so return an invalid error.
Signed-off-by: yangshiguang yangshiguang@xiaomi.com Fixes: 9af0440ec86e ("debugfs: Implement debugfs_create_str()") Cc: stable@vger.kernel.org
fs/debugfs/file.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c index 3ec3324c2060..a22ff0ceb230 100644 --- a/fs/debugfs/file.c +++ b/fs/debugfs/file.c @@ -1026,6 +1026,9 @@ ssize_t debugfs_read_file_str(struct file *file, char __user *user_buf, return ret; str = *(char **)file->private_data;
- if (!str)
return -EINVAL;What in kernel user causes this to happen? Let's fix that up instead please.
Currently I known problematic nodes in the kernel:
drivers/interconnect/debugfs-client.c: 155: debugfs_create_str("src_node", 0600, client_dir, &src_node); 156: debugfs_create_str("dst_node", 0600, client_dir, &dst_node); drivers/soundwire/debugfs.c: 362: debugfs_create_str("firmware_file", 0200, d, &firmware_file);
test case: 1. create a NULL string node char *test_node = NULL; debugfs_create_str("test_node", 0600, parent_dir, &test_node);
2. read the node, like bellow: cat /sys/kernel/debug/test_node
thanks,
greg k-h
On Mon, Dec 22, 2025 at 08:41:33PM +0800, yangshiguang wrote:
At 2025-12-22 19:54:22, "Greg KH" gregkh@linuxfoundation.org wrote:
On Mon, Dec 22, 2025 at 05:36:16PM +0800, yangshiguang1011@163.com wrote:
From: yangshiguang yangshiguang@xiaomi.com
Check in debugfs_read_file_str() if the string pointer is NULL.
When creating a node using debugfs_create_str(), the string parameter value can be NULL to indicate empty/unused/ignored.
Why would you create an empty debugfs string file? That is not ok, we should change that to not allow this.
Hi greg k-h,
Thanks for your reply.
This is due to the usage step, should write first and then read. However, there is no way to guarantee that everyone will know about this step.
True.
And debugfs_create_str() allows passing in a NULL string.
Then we should fix that :)
Therefore, when reading a NULL string, should return an invalid error instead of panic.
If you call write on a NULL string, then you could call strlen() of that NULL string, and do a memcpy out of that NULL string. All not good things, so your quick fix here really doesn't solve the root problem :(
str = *(char **)file->private_data;
- if (!str)
return -EINVAL;What in kernel user causes this to happen? Let's fix that up instead please.
Currently I known problematic nodes in the kernel:
drivers/interconnect/debugfs-client.c: 155: debugfs_create_str("src_node", 0600, client_dir, &src_node); 156: debugfs_create_str("dst_node", 0600, client_dir, &dst_node);
Ick, ok, that should be fixed.
drivers/soundwire/debugfs.c: 362: debugfs_create_str("firmware_file", 0200, d, &firmware_file);
That too should be fixed, all should just create an "empty" string to start with.
test case:
- create a NULL string node
char *test_node = NULL; debugfs_create_str("test_node", 0600, parent_dir, &test_node);
- read the node, like bellow:
cat /sys/kernel/debug/test_node
With your patch, you could change step 2 to do a write, and still cause a crash :)
So let's fix this properly, let's just fail the creation of NULL strings, and fix up all callers.
thanks,
greg k-h
linux-stable-mirror@lists.linaro.org
-
Greg KH -
yangshiguang -
yangshiguang1011＠163.com