ksmbd: fix potencial OOB in get_file_all_info() for compound requests

When a compound request consists of QUERY_DIRECTORY + QUERY_INFO
(FILE_ALL_INFORMATION) and the first command consumes nearly the entire
max_trans_size, get_file_all_info() would blindly call smbConvertToUTF16()
with PATH_MAX, causing out-of-bounds write beyond the response buffer.
In get_file_all_info(), there was a missing validation check for
the client-provided OutputBufferLength before copying the filename into
FileName field of the smb2_file_all_info structure.
If the filename length exceeds the available buffer space, it could lead to
potential buffer overflows or memory corruption during smbConvertToUTF16
conversion. This calculating the actual free buffer size using
smb2_calc_max_out_buf_len() and returning -EINVAL if the buffer is
insufficient and updating smbConvertToUTF16 to use the actual filename
length (clamped by PATH_MAX) to ensure a safe copy operation.

Cc: stable@vger.kernel.org
Fixes: e2b76ab8b5c9 ("ksmbd: add support for read compound")
Reported-by: Asim Viladi Oglu Manizada <manizada@pm.me>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

Author: namjaejeon

smb2pdu.c

@@ -5181,7 +5181,8 @@ static int get_file_all_info(struct ksmbd_work *work,
 	int conv_len;
 	char *filename;
 	u64 time;
-	int ret;
+	int ret, buf_free_len, filename_len;
+	struct smb2_query_info_req *req = ksmbd_req_buf_next(work);
 
 	if (!(fp->daccess & FILE_READ_ATTRIBUTES_LE)) {
 		ksmbd_debug(SMB, "no right to read the attributes : 0x%x\n",
@@ -5193,6 +5194,16 @@ static int get_file_all_info(struct ksmbd_work *work,
 	if (IS_ERR(filename))
 		return PTR_ERR(filename);
 
+	filename_len = strlen(filename);
+	buf_free_len = smb2_calc_max_out_buf_len(work,
+			offsetof(struct smb2_query_info_rsp, Buffer) +
+			offsetof(struct smb2_file_all_info, FileName),
+			le32_to_cpu(req->OutputBufferLength));
+	if (buf_free_len < (filename_len + 1) * 2) {
+		kfree(filename);
+		return -EINVAL;
+	}
+
 	ret = vfs_getattr(&fp->filp->f_path, &stat, STATX_BASIC_STATS,
 			  AT_STATX_SYNC_AS_STAT);
 	if (ret)
@@ -5234,7 +5245,8 @@ static int get_file_all_info(struct ksmbd_work *work,
 	file_info->Mode = fp->coption;
 	file_info->AlignmentRequirement = 0;
 	conv_len = smbConvertToUTF16((__le16 *)file_info->FileName, filename,
-				     PATH_MAX, conn->local_nls, 0);
+				     min(filename_len, PATH_MAX),
+				     conn->local_nls, 0);
 	conv_len *= 2;
 	file_info->FileNameLength = cpu_to_le32(conv_len);
 	rsp->OutputBufferLength =