Bluetooth: Fix potential bad memory access with sysfs files

commit 101545f6fef4a0a3ea8daf0b5b880df2c6a92a69 upstream.

When creating a high number of Bluetooth sockets (L2CAP, SCO
and RFCOMM) it is possible to scribble repeatedly on arbitrary
pages of memory. Ensure that the content of these sysfs files is
always less than one page. Even if this means truncating. The
files in question are scheduled to be moved over to debugfs in
the future anyway.

Based on initial patches from Neil Brown and Linus Torvalds

Reported-by: Neil Brown <neilb@suse.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

4 files changed, 41 insertions, 4 deletions

diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index 947f8bbb4bb3..62df208af94f 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -3885,16 +3885,24 @@ static ssize_t l2cap_sysfs_show(struct class *dev, char *buf)
 	struct sock *sk;
 	struct hlist_node *node;
 	char *str = buf;
+	int size = PAGE_SIZE;
 
 	read_lock_bh(&l2cap_sk_list.lock);
 
 	sk_for_each(sk, node, &l2cap_sk_list.head) {
 		struct l2cap_pinfo *pi = l2cap_pi(sk);
+		int len;
 
-		str += sprintf(str, "%s %s %d %d 0x%4.4x 0x%4.4x %d %d %d\n",
+		len = snprintf(str, size, "%s %s %d %d 0x%4.4x 0x%4.4x %d %d %d\n",
 				batostr(&bt_sk(sk)->src), batostr(&bt_sk(sk)->dst),
 				sk->sk_state, __le16_to_cpu(pi->psm), pi->scid,
 				pi->dcid, pi->imtu, pi->omtu, pi->sec_level);
+
+		size -= len;
+		if (size <= 0)
+			break;
+
+		str += len;
 	}
 
 	read_unlock_bh(&l2cap_sk_list.lock);
diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index b3bcd4bffb2e..ef3abf28c120 100644
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -2096,6 +2096,7 @@ static ssize_t rfcomm_dlc_sysfs_show(struct class *dev, char *buf)
 	struct rfcomm_session *s;
 	struct list_head *pp, *p;
 	char *str = buf;
+	int size = PAGE_SIZE;
 
 	rfcomm_lock();
 
@@ -2104,11 +2105,21 @@ static ssize_t rfcomm_dlc_sysfs_show(struct class *dev, char *buf)
 		list_for_each(pp, &s->dlcs) {
 			struct sock *sk = s->sock->sk;
 			struct rfcomm_dlc *d = list_entry(pp, struct rfcomm_dlc, list);
+			int len;
 
-			str += sprintf(str, "%s %s %ld %d %d %d %d\n",
+			len = snprintf(str, size, "%s %s %ld %d %d %d %d\n",
 					batostr(&bt_sk(sk)->src), batostr(&bt_sk(sk)->dst),
 					d->state, d->dlci, d->mtu, d->rx_credits, d->tx_credits);
+
+			size -= len;
+			if (size <= 0)
+				break;
+
+			str += len;
 		}
+
+		if (size <= 0)
+			break;
 	}
 
 	rfcomm_unlock();
diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c
index 8a20aaf1f231..30a36499ee77 100644
--- a/net/bluetooth/rfcomm/sock.c
+++ b/net/bluetooth/rfcomm/sock.c
@@ -1065,13 +1065,22 @@ static ssize_t rfcomm_sock_sysfs_show(struct class *dev, char *buf)
 	struct sock *sk;
 	struct hlist_node *node;
 	char *str = buf;
+	int size = PAGE_SIZE;
 
 	read_lock_bh(&rfcomm_sk_list.lock);
 
 	sk_for_each(sk, node, &rfcomm_sk_list.head) {
-		str += sprintf(str, "%s %s %d %d\n",
+		int len;
+
+		len = snprintf(str, size, "%s %s %d %d\n",
 				batostr(&bt_sk(sk)->src), batostr(&bt_sk(sk)->dst),
 				sk->sk_state, rfcomm_pi(sk)->channel);
+
+		size -= len;
+		if (size <= 0)
+			break;
+
+		str += len;
 	}
 
 	read_unlock_bh(&rfcomm_sk_list.lock);
diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index 77f4153bdb5e..5c0685eba947 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -957,13 +957,22 @@ static ssize_t sco_sysfs_show(struct class *dev, char *buf)
 	struct sock *sk;
 	struct hlist_node *node;
 	char *str = buf;
+	int size = PAGE_SIZE;
 
 	read_lock_bh(&sco_sk_list.lock);
 
 	sk_for_each(sk, node, &sco_sk_list.head) {
-		str += sprintf(str, "%s %s %d\n",
+		int len;
+
+		len = snprintf(str, size, "%s %s %d\n",
 				batostr(&bt_sk(sk)->src), batostr(&bt_sk(sk)->dst),
 				sk->sk_state);
+
+		size -= len;
+		if (size <= 0)
+			break;
+
+		str += len;
 	}
 
 	read_unlock_bh(&sco_sk_list.lock);