linux-kernel - [PATCH 6/7] cifs: Validate content of native symlink

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Message-Id: <20240929185053.10554-7-pali@kernel.org>
Date: Sun, 29 Sep 2024 20:50:52 +0200
From: Pali Rohár <pali@...nel.org>
To: Steve French <sfrench@...ba.org>,
	Paulo Alcantara <pc@...guebit.com>,
	Ronnie Sahlberg <ronniesahlberg@...il.com>
Cc: linux-cifs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 6/7] cifs: Validate content of native symlink

Check that buffer does not contain UTF-16 null codepoint
because Linux cannot process symlink with null byte.

Signed-off-by: Pali Rohár <pali@...nel.org>
---
 fs/smb/client/reparse.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/smb/client/reparse.c b/fs/smb/client/reparse.c
index 5a738f65b190..ca4f96c43508 100644
--- a/fs/smb/client/reparse.c
+++ b/fs/smb/client/reparse.c
@@ -509,6 +509,16 @@ int smb2_parse_native_symlink(char **target, const char *buf, unsigned int len,
 	int rc;
 	int i;
 
+	/*
+	 * Check that buffer does not contain UTF-16 null codepoint
+	 * because Linux cannot process symlink with null byte.
+	 */
+	if (unicode && UniStrnlen((wchar_t *)buf, len/2) != len/2) {
+		cifs_dbg(VFS, "srv returned null byte in native symlink target location\n");
+		rc = -EIO;
+		goto out;
+	}
+
 	smb_target = cifs_strndup_from_utf16(buf, len, unicode, cifs_sb->local_nls);
 	if (!smb_target) {
 		rc = -ENOMEM;
-- 
2.20.1