[PATCH v5] Bluetooth: bnep: reject short frames before parsing

[Zhang Cen <rollkingzzc@gmail.com>]

A BNEP peer can send a short BNEP SDU. bnep_rx_frame() reads the
packet type byte immediately and, for control packets, reads the control
opcode and setup UUID-size byte before proving that those bytes are
present. bnep_rx_control() also dereferences the control opcode without
rejecting an empty control payload.

Use skb_pull_data() for the fixed fields in bnep_rx_frame() so a NULL
return gates each dereference. Split the control handler so the frame
path can pass an opcode that has already been pulled, and keep the
byte-buffer wrapper for extension control payloads.

For BNEP_SETUP_CONN_REQ, name the UUID-size byte before pulling the
setup payload. struct bnep_setup_conn_req carries destination and source
service UUIDs after that byte, each uuid_size bytes, so the parser now
documents that tuple explicitly instead of leaving the pull length as an
opaque multiplication.

Validation reproduced this kernel report:
KASAN slab-out-of-bounds in bnep_rx_frame.isra.0+0x130c/0x1790
The buggy address belongs to the object at ffff88800c0f7908 which belongs
to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes to the right of allocated 1-byte
region [ffff88800c0f7908, ffff88800c0f7909)
Read of size 1
Call trace:
  dump_stack_lvl+0xb3/0x140 (?:?)
  print_address_description+0x57/0x3a0 (?:?)
  bnep_rx_frame+0x130c/0x1790 (net/bluetooth/bnep/core.c:306)
  print_report+0xb9/0x2b0 (?:?)
  __virt_addr_valid+0x1ba/0x3a0 (?:?)
  srso_alias_return_thunk+0x5/0xfbef5 (?:?)
  kasan_addr_to_slab+0x21/0x60 (?:?)
  kasan_report+0xe0/0x110 (?:?)
  process_one_work+0xfce/0x17e0 (kernel/workqueue.c:3200)
  worker_thread+0x65c/0xe40 (?:?)
  __kthread_parkme+0x184/0x230 (?:?)
  kthread+0x35e/0x470 (?:?)
  _raw_spin_unlock_irq+0x28/0x50 (?:?)
  ret_from_fork+0x586/0x870 (?:?)
  __switch_to+0x74f/0xdc0 (?:?)
  ret_from_fork_asm+0x1a/0x30 (?:?)

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Assisted-by: Codex:gpt-5.5
Signed-off-by: Zhang Cen <rollkingzzc@gmail.com>
---
v5:
Clarify the BNEP_SETUP_CONN_REQ UUID-size handling using the setup
request layout from struct bnep_setup_conn_req.

v4:
Wrap the changelog entry that Bluetooth CI flagged as overlong.
Keep the BNEP code fix unchanged from the last submitted patch.

v3:
Use skb_pull_data() with NULL checks in bnep_rx_frame() instead of direct
skb->len guards before fixed header dereferences.
Split control handling so bnep_rx_frame() can pass an already pulled control
opcode while preserving the existing extension control wrapper.

 net/bluetooth/bnep/core.c | 57 ++++++++++++++++++++++++---------------
 1 file changed, 36 insertions(+), 21 deletions(-)

diff --git a/net/bluetooth/bnep/core.c b/net/bluetooth/bnep/core.c
index 0de5df690bd0..5c5f53ff30e8 100644
--- a/net/bluetooth/bnep/core.c
+++ b/net/bluetooth/bnep/core.c
@@ -206,14 +206,11 @@ static int bnep_ctrl_set_mcfilter(struct bnep_session *s, u8 *data, int len)
 	return 0;
 }
 
-static int bnep_rx_control(struct bnep_session *s, void *data, int len)
+static int bnep_rx_control_cmd(struct bnep_session *s, u8 cmd, void *data,
+			       int len)
 {
-	u8  cmd = *(u8 *)data;
 	int err = 0;
 
-	data++;
-	len--;
-
 	switch (cmd) {
 	case BNEP_CMD_NOT_UNDERSTOOD:
 	case BNEP_SETUP_CONN_RSP:
@@ -254,6 +251,14 @@ static int bnep_rx_control(struct bnep_session *s, void *data, int len)
 	return err;
 }
 
+static int bnep_rx_control(struct bnep_session *s, void *data, int len)
+{
+	if (len < 1)
+		return -EILSEQ;
+
+	return bnep_rx_control_cmd(s, *(u8 *)data, data + 1, len - 1);
+}
+
 static int bnep_rx_extension(struct bnep_session *s, struct sk_buff *skb)
 {
 	struct bnep_ext_hdr *h;
@@ -299,19 +304,26 @@ static int bnep_rx_frame(struct bnep_session *s, struct sk_buff *skb)
 {
 	struct net_device *dev = s->dev;
 	struct sk_buff *nskb;
+	u8 *data;
 	u8 type, ctrl_type;
 
 	dev->stats.rx_bytes += skb->len;
 
-	type = *(u8 *) skb->data;
-	skb_pull(skb, 1);
-	ctrl_type = *(u8 *)skb->data;
+	data = skb_pull_data(skb, sizeof(type));
+	if (!data)
+		goto badframe;
+	type = *data;
 
 	if ((type & BNEP_TYPE_MASK) >= sizeof(__bnep_rx_hlen))
 		goto badframe;
 
 	if ((type & BNEP_TYPE_MASK) == BNEP_CONTROL) {
-		if (bnep_rx_control(s, skb->data, skb->len) < 0) {
+		data = skb_pull_data(skb, sizeof(ctrl_type));
+		if (!data)
+			goto badframe;
+		ctrl_type = *data;
+
+		if (bnep_rx_control_cmd(s, ctrl_type, skb->data, skb->len) < 0) {
 			dev->stats.tx_errors++;
 			kfree_skb(skb);
 			return 0;
@@ -324,24 +336,27 @@ static int bnep_rx_frame(struct bnep_session *s, struct sk_buff *skb)
 
 		/* Verify and pull ctrl message since it's already processed */
 		switch (ctrl_type) {
-		case BNEP_SETUP_CONN_REQ:
-			/* Pull: ctrl type (1 b), len (1 b), data (len bytes) */
-			if (!skb_pull(skb, 2 + *(u8 *)(skb->data + 1) * 2))
+		case BNEP_SETUP_CONN_REQ: {
+			u8 uuid_size;
+
+			/* Pull uuid_size and the dst/src service UUIDs. */
+			data = skb_pull_data(skb, sizeof(uuid_size));
+			if (!data)
+				goto badframe;
+			uuid_size = *data;
+			if (!skb_pull(skb, uuid_size + uuid_size))
 				goto badframe;
 			break;
+		}
 		case BNEP_FILTER_MULTI_ADDR_SET:
-		case BNEP_FILTER_NET_TYPE_SET: {
-			u8 *hdr;
-
-			/* Pull ctrl type (1 b) + len (2 b) */
-			hdr = skb_pull_data(skb, 3);
-			if (!hdr)
+		case BNEP_FILTER_NET_TYPE_SET:
+			/* Pull: len (2 b), data (len bytes) */
+			data = skb_pull_data(skb, sizeof(u16));
+			if (!data)
 				goto badframe;
-			/* Pull data (len bytes); length is big-endian */
-			if (!skb_pull(skb, get_unaligned_be16(&hdr[1])))
+			if (!skb_pull(skb, get_unaligned_be16(data)))
 				goto badframe;
 			break;
-		}
 		default:
 			kfree_skb(skb);
 			return 0;
-- 
2.43.0