cifs: Fix stack out-of-bounds in smb{2,3}_create_lease_buf()

smb{2,3}_create_lease_buf() store a lease key in the lease
context for later usage on a lease break.

In most paths, the key is currently sourced from data that
happens to be on the stack near local variables for oplock in
SMB2_open() callers, e.g. from open_shroot(), whereas
smb2_open_file() properly allocates space on its stack for it.

The address of those local variables holding the oplock is then
passed to create_lease_buf handlers via SMB2_open(), and 16
bytes near oplock are used. This causes a stack out-of-bounds
access as reported by KASAN on SMB2.1 and SMB3 mounts (first
out-of-bounds access is shown here):

[  111.528823] BUG: KASAN: stack-out-of-bounds in smb3_create_lease_buf+0x399/0x3b0 [cifs]
[  111.530815] Read of size 8 at addr ffff88010829f249 by task mount.cifs/985
[  111.532838] CPU: 3 PID: 985 Comm: mount.cifs Not tainted 4.18.0-rc3+ #91
[  111.534656] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[  111.536838] Call Trace:
[  111.537528]  dump_stack+0xc2/0x16b
[  111.540890]  print_address_description+0x6a/0x270
[  111.542185]  kasan_report+0x258/0x380
[  111.544701]  smb3_create_lease_buf+0x399/0x3b0 [cifs]
[  111.546134]  SMB2_open+0x1ef8/0x4b70 [cifs]
[  111.575883]  open_shroot+0x339/0x550 [cifs]
[  111.591969]  smb3_qfs_tcon+0x32c/0x1e60 [cifs]
[  111.617405]  cifs_mount+0x4f3/0x2fc0 [cifs]
[  111.674332]  cifs_smb3_do_mount+0x263/0xf10 [cifs]
[  111.677915]  mount_fs+0x55/0x2b0
[  111.679504]  vfs_kern_mount.part.22+0xaa/0x430
[  111.684511]  do_mount+0xc40/0x2660
[  111.698301]  ksys_mount+0x80/0xd0
[  111.701541]  do_syscall_64+0x14e/0x4b0
[  111.711807]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[  111.713665] RIP: 0033:0x7f372385b5fa
[  111.715311] Code: 48 8b 0d 99 78 2c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 66 78 2c 00 f7 d8 64 89 01 48
[  111.720330] RSP: 002b:00007ffff27049d8 EFLAGS: 00000206 ORIG_RAX: 00000000000000a5
[  111.722601] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f372385b5fa
[  111.724842] RDX: 000055c2ecdc73b2 RSI: 000055c2ecdc73f9 RDI: 00007ffff270580f
[  111.727083] RBP: 00007ffff2705804 R08: 000055c2ee976060 R09: 0000000000001000
[  111.729319] R10: 0000000000000000 R11: 0000000000000206 R12: 00007f3723f4d000
[  111.731615] R13: 000055c2ee976060 R14: 00007f3723f4f90f R15: 0000000000000000

[  111.735448] The buggy address belongs to the page:
[  111.737420] page:ffffea000420a7c0 count:0 mapcount:0 mapping:0000000000000000 index:0x0
[  111.739890] flags: 0x17ffffc0000000()
[  111.741750] raw: 0017ffffc0000000 0000000000000000 dead000000000200 0000000000000000
[  111.744216] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
[  111.746679] page dumped because: kasan: bad access detected

[  111.750482] Memory state around the buggy address:
[  111.752562]  ffff88010829f100: 00 f2 f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00 00
[  111.754991]  ffff88010829f180: 00 00 f2 f2 00 00 00 00 00 00 00 00 00 00 00 00
[  111.757401] >ffff88010829f200: 00 00 00 00 00 f1 f1 f1 f1 01 f2 f2 f2 f2 f2 f2
[  111.759801]                                               ^
[  111.762034]  ffff88010829f280: f2 02 f2 f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00
[  111.764486]  ffff88010829f300: f2 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[  111.766913] ==================================================================

Lease keys are however already generated and stored in fid data
on open and create paths: pass them down to the lease context
creation handlers and use them.

Suggested-by: Aurélien Aptel <aaptel@suse.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Fixes: b8c32dbb0deb ("CIFS: Request SMB2.1 leases")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifsglob.h

@@ -423,7 +423,7 @@ struct smb_version_operations {
 	void (*set_oplock_level)(struct cifsInodeInfo *, __u32, unsigned int,
 				 bool *);
 	/* create lease context buffer for CREATE request */
-	char * (*create_lease_buf)(u8 *, u8);
+	char * (*create_lease_buf)(u8 *lease_key, u8 oplock);
 	/* parse lease context buffer and return oplock/epoch info */
 	__u8 (*parse_lease_buf)(void *buf, unsigned int *epoch, char *lkey);
 	ssize_t (*copychunk_range)(const unsigned int,

fs/cifs/smb2file.c

@@ -41,7 +41,7 @@ smb2_open_file(const unsigned int xid, struct cifs_open_parms *oparms,
 	int rc;
 	__le16 *smb2_path;
 	struct smb2_file_all_info *smb2_data = NULL;
-	__u8 smb2_oplock[17];
+	__u8 smb2_oplock;
 	struct cifs_fid *fid = oparms->fid;
 	struct network_resiliency_req nr_ioctl_req;
 
@@ -59,12 +59,9 @@ smb2_open_file(const unsigned int xid, struct cifs_open_parms *oparms,
 	}
 
 	oparms->desired_access |= FILE_READ_ATTRIBUTES;
-	*smb2_oplock = SMB2_OPLOCK_LEVEL_BATCH;
+	smb2_oplock = SMB2_OPLOCK_LEVEL_BATCH;
 
-	if (oparms->tcon->ses->server->capabilities & SMB2_GLOBAL_CAP_LEASING)
-		memcpy(smb2_oplock + 1, fid->lease_key, SMB2_LEASE_KEY_SIZE);
-
-	rc = SMB2_open(xid, oparms, smb2_path, smb2_oplock, smb2_data, NULL,
+	rc = SMB2_open(xid, oparms, smb2_path, &smb2_oplock, smb2_data, NULL,
 		       NULL);
 	if (rc)
 		goto out;
@@ -101,7 +98,7 @@ smb2_open_file(const unsigned int xid, struct cifs_open_parms *oparms,
 		move_smb2_info_to_cifs(buf, smb2_data);
 	}
 
-	*oplock = *smb2_oplock;
+	*oplock = smb2_oplock;
 out:
 	kfree(smb2_data);
 	kfree(smb2_path);

fs/cifs/smb2ops.c

@@ -2222,8 +2222,7 @@ smb2_create_lease_buf(u8 *lease_key, u8 oplock)
 	if (!buf)
 		return NULL;
 
-	buf->lcontext.LeaseKeyLow = cpu_to_le64(*((u64 *)lease_key));
-	buf->lcontext.LeaseKeyHigh = cpu_to_le64(*((u64 *)(lease_key + 8)));
+	memcpy(&buf->lcontext.LeaseKey, lease_key, SMB2_LEASE_KEY_SIZE);
 	buf->lcontext.LeaseState = map_oplock_to_lease(oplock);
 
 	buf->ccontext.DataOffset = cpu_to_le16(offsetof
@@ -2249,8 +2248,7 @@ smb3_create_lease_buf(u8 *lease_key, u8 oplock)
 	if (!buf)
 		return NULL;
 
-	buf->lcontext.LeaseKeyLow = cpu_to_le64(*((u64 *)lease_key));
-	buf->lcontext.LeaseKeyHigh = cpu_to_le64(*((u64 *)(lease_key + 8)));
+	memcpy(&buf->lcontext.LeaseKey, lease_key, SMB2_LEASE_KEY_SIZE);
 	buf->lcontext.LeaseState = map_oplock_to_lease(oplock);
 
 	buf->ccontext.DataOffset = cpu_to_le16(offsetof
@@ -2287,8 +2285,7 @@ smb3_parse_lease_buf(void *buf, unsigned int *epoch, char *lease_key)
 	if (lc->lcontext.LeaseFlags & SMB2_LEASE_FLAG_BREAK_IN_PROGRESS)
 		return SMB2_OPLOCK_LEVEL_NOCHANGE;
 	if (lease_key)
-		memcpy(lease_key, &lc->lcontext.LeaseKeyLow,
-		       SMB2_LEASE_KEY_SIZE);
+		memcpy(lease_key, &lc->lcontext.LeaseKey, SMB2_LEASE_KEY_SIZE);
 	return le32_to_cpu(lc->lcontext.LeaseState);
 }
 

fs/cifs/smb2pdu.c

@@ -1716,12 +1716,12 @@ parse_lease_state(struct TCP_Server_Info *server, struct smb2_create_rsp *rsp,
 
 static int
 add_lease_context(struct TCP_Server_Info *server, struct kvec *iov,
-		  unsigned int *num_iovec, __u8 *oplock)
+		  unsigned int *num_iovec, u8 *lease_key, __u8 *oplock)
 {
 	struct smb2_create_req *req = iov[0].iov_base;
 	unsigned int num = *num_iovec;
 
-	iov[num].iov_base = server->ops->create_lease_buf(oplock+1, *oplock);
+	iov[num].iov_base = server->ops->create_lease_buf(lease_key, *oplock);
 	if (iov[num].iov_base == NULL)
 		return -ENOMEM;
 	iov[num].iov_len = server->vals->create_lease_size;
@@ -2181,7 +2181,8 @@ SMB2_open(const unsigned int xid, struct cifs_open_parms *oparms, __le16 *path,
 	    *oplock == SMB2_OPLOCK_LEVEL_NONE)
 		req->RequestedOplockLevel = *oplock;
 	else {
-		rc = add_lease_context(server, iov, &n_iov, oplock);
+		rc = add_lease_context(server, iov, &n_iov,
+				       oparms->fid->lease_key, oplock);
 		if (rc) {
 			cifs_small_buf_release(req);
 			kfree(copy_path);

fs/cifs/smb2pdu.h

@@ -678,16 +678,14 @@ struct create_context {
 #define SMB2_LEASE_KEY_SIZE 16
 
 struct lease_context {
-	__le64 LeaseKeyLow;
-	__le64 LeaseKeyHigh;
+	u8 LeaseKey[SMB2_LEASE_KEY_SIZE];
 	__le32 LeaseState;
 	__le32 LeaseFlags;
 	__le64 LeaseDuration;
 } __packed;
 
 struct lease_context_v2 {
-	__le64 LeaseKeyLow;
-	__le64 LeaseKeyHigh;
+	u8 LeaseKey[SMB2_LEASE_KEY_SIZE];
 	__le32 LeaseState;
 	__le32 LeaseFlags;
 	__le64 LeaseDuration;