From 86b5488121db563b33684f56aafa62156f764be3 Mon Sep 17 00:00:00 2001 From: Mike Tipton Date: Mon, 7 Aug 2023 07:29:12 -0700 Subject: debugfs: Add write support to debugfs_create_str() 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@hirez.programming.kicks-ass.net/ Signed-off-by: Mike Tipton Acked-by: Greg Kroah-Hartman Link: https://lore.kernel.org/r/20230807142914.12480-2-quic_mdtipton@quicinc.com Signed-off-by: Georgi Djakov --- fs/debugfs/file.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 46 insertions(+), 2 deletions(-) (limited to 'fs/debugfs') 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; } static const struct file_operations fops_str = { -- cgit