On Fri, Aug 18, 2023 at 01:05:57PM +0300, Georgi Djakov wrote: > Hi Greg, > > 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 true. Write support is added only for debugfs string files that are > created with +w permissions. All existing files are created as read-only > and use the fops_str_ro ops. > > > I recommend just using your own debugfs file function instead, as this > > could cause bad problems, right? Are you sure that all string calls can > > handle the variable be freed underneath it like this call will allow to > > happen? > > > > So I wouldn't recommend doing this, sorry. > > > > Maybe you missed the fact that the different file ops are already there > and are selected based on permissions: > > > static const struct file_operations fops_str = { > > .read = debugfs_read_file_str, > > .write = debugfs_write_file_str, > > .open = simple_open, > > .llseek = default_llseek, > > }; > > > > static const struct file_operations fops_str_ro = { > > .read = debugfs_read_file_str, > > .open = simple_open, > > .llseek = default_llseek, > > }; > > > > static const struct file_operations fops_str_wo = { > > .write = debugfs_write_file_str, > > .open = simple_open, > > .llseek = default_llseek, > > }; > > ...so this patch is doing exactly what you suggested? If you agree, > could you ack it again please? Yes, I did miss that, sorry, my appologies for dragging this out so long: Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
