ksmbd: replace one-element array with flex-array member in struct smb2_ea_info

UBSAN complains about out-of-bounds array indexes on 1-element arrays in
struct smb2_ea_info.

UBSAN: array-index-out-of-bounds in fs/smb/server/smb2pdu.c:4335:15
index 1 is out of range for type 'char [1]'
CPU: 1 PID: 354 Comm: kworker/1:4 Not tainted 6.5.0-rc4 #1
Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop
Reference Platform, BIOS 6.00 07/22/2020
Workqueue: ksmbd-io handle_ksmbd_work [ksmbd]
Call Trace:
 <TASK>
 __dump_stack linux/lib/dump_stack.c:88
 dump_stack_lvl+0x48/0x70 linux/lib/dump_stack.c:106
 dump_stack+0x10/0x20 linux/lib/dump_stack.c:113
 ubsan_epilogue linux/lib/ubsan.c:217
 __ubsan_handle_out_of_bounds+0xc6/0x110 linux/lib/ubsan.c:348
 smb2_get_ea linux/fs/smb/server/smb2pdu.c:4335
 smb2_get_info_file linux/fs/smb/server/smb2pdu.c:4900
 smb2_query_info+0x63ae/0x6b20 linux/fs/smb/server/smb2pdu.c:5275
 __process_request linux/fs/smb/server/server.c:145
 __handle_ksmbd_work linux/fs/smb/server/server.c:213
 handle_ksmbd_work+0x348/0x10b0 linux/fs/smb/server/server.c:266
 process_one_work+0x85a/0x1500 linux/kernel/workqueue.c:2597
 worker_thread+0xf3/0x13a0 linux/kernel/workqueue.c:2748
 kthread+0x2b7/0x390 linux/kernel/kthread.c:389
 ret_from_fork+0x44/0x90 linux/arch/x86/kernel/process.c:145
 ret_from_fork_asm+0x1b/0x30 linux/arch/x86/entry/entry_64.S:304
 </TASK>

Cc: stable@vger.kernel.org
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: namjaejeon

fs/smb/server/smb2pdu.c

@@ -4335,7 +4335,7 @@ static int smb2_get_ea(struct ksmbd_work *work, struct ksmbd_file *fp,
 		if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
 			name_len -= XATTR_USER_PREFIX_LEN;
 
-		ptr = (char *)(&eainfo->name + name_len + 1);
+		ptr = eainfo->name + name_len + 1;
 		buf_free_len -= (offsetof(struct smb2_ea_info, name) +
 				name_len + 1);
 		/* bailout if xattr can't fit in buf_free_len */

fs/smb/server/smb2pdu.h

@@ -361,7 +361,7 @@ struct smb2_ea_info {
 	__u8   Flags;
 	__u8   EaNameLength;
 	__le16 EaValueLength;
-	char name[1];
+	char name[];
 	/* optionally followed by value */
 } __packed; /* level 15 Query */