linux-kernel - [PATCH 1/3] debugfs: Add write support to debugfs_create

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20230725012859.18474-2-quic_mdtipton@quicinc.com>
Date:   Mon, 24 Jul 2023 18:28:57 -0700
From:   Mike Tipton <quic_mdtipton@...cinc.com>
To:     <djakov@...nel.org>, <gregkh@...uxfoundation.org>,
        <rafael@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        <quic_okukatla@...cinc.com>, <quic_viveka@...cinc.com>,
        Mike Tipton <quic_mdtipton@...cinc.com>
Subject: [PATCH 1/3] debugfs: Add write support to debugfs_create_str()

Implementation taken from original patch series that added
debugfs_create_str() [0]. Write support was present in the initial patch
revisions, but was later removed 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 <quic_mdtipton@...cinc.com>
---
 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;
 }
 
 static const struct file_operations fops_str = {
-- 
2.17.1