libceph: do not hard code max auth ticket len

We hard code cephx auth ticket buffer size to 256 bytes.  This isn't
enough for any moderate setups and, in case tickets themselves are not
encrypted, leads to buffer overflows (ceph_x_decrypt() errors out, but
ceph_decode_copy() doesn't - it's just a memcpy() wrapper).  Since the
buffer is allocated dynamically anyway, allocated it a bit later, at
the point where we know how much is going to be needed.

Fixes: http://tracker.ceph.com/issues/8979

Cc: stable@vger.kernel.org
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Sage Weil <sage@redhat.com>

net/ceph/auth_x.c

@@ -13,8 +13,6 @@
 #include "auth_x.h"
 #include "auth_x_protocol.h"
 
-#define TEMP_TICKET_BUF_LEN	256
-
 static void ceph_x_validate_tickets(struct ceph_auth_client *ac, int *pneed);
 
 static int ceph_x_is_authenticated(struct ceph_auth_client *ac)
@@ -64,7 +62,7 @@ static int ceph_x_encrypt(struct ceph_crypto_key *secret,
 }
 
 static int ceph_x_decrypt(struct ceph_crypto_key *secret,
-			  void **p, void *end, void *obuf, size_t olen)
+			  void **p, void *end, void **obuf, size_t olen)
 {
 	struct ceph_x_encrypt_header head;
 	size_t head_len = sizeof(head);
@@ -75,8 +73,14 @@ static int ceph_x_decrypt(struct ceph_crypto_key *secret,
 		return -EINVAL;
 
 	dout("ceph_x_decrypt len %d\n", len);
-	ret = ceph_decrypt2(secret, &head, &head_len, obuf, &olen,
-			    *p, len);
+	if (*obuf == NULL) {
+		*obuf = kmalloc(len, GFP_NOFS);
+		if (!*obuf)
+			return -ENOMEM;
+		olen = len;
+	}
+
+	ret = ceph_decrypt2(secret, &head, &head_len, *obuf, &olen, *p, len);
 	if (ret)
 		return ret;
 	if (head.struct_v != 1 || le64_to_cpu(head.magic) != CEPHX_ENC_MAGIC)
@@ -131,18 +135,19 @@ static void remove_ticket_handler(struct ceph_auth_client *ac,
 
 static int process_one_ticket(struct ceph_auth_client *ac,
 			      struct ceph_crypto_key *secret,
-			      void **p, void *end,
-			      void *dbuf, void *ticket_buf)
+			      void **p, void *end)
 {
 	struct ceph_x_info *xi = ac->private;
 	int type;
 	u8 tkt_struct_v, blob_struct_v;
 	struct ceph_x_ticket_handler *th;
+	void *dbuf = NULL;
 	void *dp, *dend;
 	int dlen;
 	char is_enc;
 	struct timespec validity;
 	struct ceph_crypto_key old_key;
+	void *ticket_buf = NULL;
 	void *tp, *tpend;
 	struct ceph_timespec new_validity;
 	struct ceph_crypto_key new_session_key;
@@ -167,8 +172,7 @@ static int process_one_ticket(struct ceph_auth_client *ac,
 	}
 
 	/* blob for me */
-	dlen = ceph_x_decrypt(secret, p, end, dbuf,
-			      TEMP_TICKET_BUF_LEN);
+	dlen = ceph_x_decrypt(secret, p, end, &dbuf, 0);
 	if (dlen <= 0) {
 		ret = dlen;
 		goto out;
@@ -195,20 +199,25 @@ static int process_one_ticket(struct ceph_auth_client *ac,
 
 	/* ticket blob for service */
 	ceph_decode_8_safe(p, end, is_enc, bad);
-	tp = ticket_buf;
 	if (is_enc) {
 		/* encrypted */
 		dout(" encrypted ticket\n");
-		dlen = ceph_x_decrypt(&old_key, p, end, ticket_buf,
-				      TEMP_TICKET_BUF_LEN);
+		dlen = ceph_x_decrypt(&old_key, p, end, &ticket_buf, 0);
 		if (dlen < 0) {
 			ret = dlen;
 			goto out;
 		}
+		tp = ticket_buf;
 		dlen = ceph_decode_32(&tp);
 	} else {
 		/* unencrypted */
 		ceph_decode_32_safe(p, end, dlen, bad);
+		ticket_buf = kmalloc(dlen, GFP_NOFS);
+		if (!ticket_buf) {
+			ret = -ENOMEM;
+			goto out;
+		}
+		tp = ticket_buf;
 		ceph_decode_need(p, end, dlen, bad);
 		ceph_decode_copy(p, ticket_buf, dlen);
 	}
@@ -237,6 +246,8 @@ static int process_one_ticket(struct ceph_auth_client *ac,
 	xi->have_keys |= th->service;
 
 out:
+	kfree(ticket_buf);
+	kfree(dbuf);
 	return ret;
 
 bad:
@@ -249,21 +260,10 @@ static int ceph_x_proc_ticket_reply(struct ceph_auth_client *ac,
 				    void *buf, void *end)
 {
 	void *p = buf;
-	char *dbuf;
-	char *ticket_buf;
 	u8 reply_struct_v;
 	u32 num;
 	int ret;
 
-	dbuf = kmalloc(TEMP_TICKET_BUF_LEN, GFP_NOFS);
-	if (!dbuf)
-		return -ENOMEM;
-
-	ret = -ENOMEM;
-	ticket_buf = kmalloc(TEMP_TICKET_BUF_LEN, GFP_NOFS);
-	if (!ticket_buf)
-		goto out_dbuf;
-
 	ceph_decode_8_safe(&p, end, reply_struct_v, bad);
 	if (reply_struct_v != 1)
 		return -EINVAL;
@@ -272,22 +272,15 @@ static int ceph_x_proc_ticket_reply(struct ceph_auth_client *ac,
 	dout("%d tickets\n", num);
 
 	while (num--) {
-		ret = process_one_ticket(ac, secret, &p, end,
-					 dbuf, ticket_buf);
+		ret = process_one_ticket(ac, secret, &p, end);
 		if (ret)
-			goto out;
+			return ret;
 	}
 
-	ret = 0;
-out:
-	kfree(ticket_buf);
-out_dbuf:
-	kfree(dbuf);
-	return ret;
+	return 0;
 
 bad:
-	ret = -EINVAL;
-	goto out;
+	return -EINVAL;
 }
 
 static int ceph_x_build_authorizer(struct ceph_auth_client *ac,
@@ -603,13 +596,14 @@ static int ceph_x_verify_authorizer_reply(struct ceph_auth_client *ac,
 	struct ceph_x_ticket_handler *th;
 	int ret = 0;
 	struct ceph_x_authorize_reply reply;
+	void *preply = &reply;
 	void *p = au->reply_buf;
 	void *end = p + sizeof(au->reply_buf);
 
 	th = get_ticket_handler(ac, au->service);
 	if (IS_ERR(th))
 		return PTR_ERR(th);
-	ret = ceph_x_decrypt(&th->session_key, &p, end, &reply, sizeof(reply));
+	ret = ceph_x_decrypt(&th->session_key, &p, end, &preply, sizeof(reply));
 	if (ret < 0)
 		return ret;
 	if (ret != sizeof(reply))