Hi Greg,
Thanks for the comments!
On 12.08.23 13:40, Greg KH wrote:
On Mon, Aug 07, 2023 at 07:29:12AM -0700, Mike Tipton wrote:
Currently, debugfs_create_str() only supports reading strings from
debugfs. Add support for writing them as well.
Based on original implementation by Peter Zijlstra [0]. Write support
was present in the initial patch version, but dropped in v2 due to lack
of users. We have a user now, so reintroduce it.
[0] https://lore.kernel.org/all/YF3Hv5zXb%2F6lauzs@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
Signed-off-by: Mike Tipton <quic_mdtipton@xxxxxxxxxxx>
---
fs/debugfs/file.c | 48 +++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 46 insertions(+), 2 deletions(-)
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index b7711888dd17..87b3753aa4b1 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -904,8 +904,52 @@ EXPORT_SYMBOL_GPL(debugfs_create_str);
static ssize_t debugfs_write_file_str(struct file *file, const char __user *user_buf,
size_t count, loff_t *ppos)
{
- /* This is really only for read-only strings */
- return -EINVAL;
+ struct dentry *dentry = F_DENTRY(file);
+ char *old, *new = NULL;
+ int pos = *ppos;
+ int r;
+
+ r = debugfs_file_get(dentry);
+ if (unlikely(r))
+ return r;
+
+ old = *(char **)file->private_data;
+
+ /* only allow strict concatenation */
+ r = -EINVAL;
+ if (pos && pos != strlen(old))
+ goto error;
+
+ r = -E2BIG;
+ if (pos + count + 1 > PAGE_SIZE)
+ goto error;
+
+ r = -ENOMEM;
+ new = kmalloc(pos + count + 1, GFP_KERNEL);
+ if (!new)
+ goto error;
+
+ if (pos)
+ memcpy(new, old, pos);
+
+ r = -EFAULT;
+ if (copy_from_user(new + pos, user_buf, count))
+ goto error;
+
+ new[pos + count] = '\0';
+ strim(new);
+
+ rcu_assign_pointer(*(char **)file->private_data, new);
+ synchronize_rcu();
+ kfree(old);
+
+ debugfs_file_put(dentry);
+ return count;
+
+error:
+ kfree(new);
+ debugfs_file_put(dentry);
+ return r;
}
So you just added write support for ALL debugfs files that use the
string interface, what did you just allow to break?
Not really. According to the existing code, the write support for strings
is enabled only when the file is created with +w permissions. For read-only
files, we use fops_str_ro, which is the case for all existing string files:
$ git grep -w debugfs_create_str | egrep -v "fs/debugfs/file.c|include/linux/debugfs.h"
drivers/firmware/arm_scmi/driver.c: debugfs_create_str("instance_name", 0400, top_dentry,
drivers/firmware/arm_scmi/driver.c: debugfs_create_str("type", 0400, trans, (char **)&dbg->type);
drivers/opp/debugfs.c: debugfs_create_str("of_name", S_IRUGO, d, (char **)&opp->of_name);
For fops_str_ro, the .write function is not implemented, so nothing should break?
I recommend just using your own debugfs file function instead, as this
could cause bad problems, right?
Agree, and that should be exactly what this patch does.
Are you sure that all string calls can
handle the variable be freed underneath it like this call will allow to
happen?
Looks fine, at least for this patch-set.
Thanks,
Georgi
