[PATCH net v2 1/4] ieee802154: cc2520: ensure tailroom before skb_put() in promiscuous TX

In cc2520_tx(), when priv->promiscuous is enabled, skb_put(skb, 2) is
called unconditionally to append the 2-byte software CRC without checking
whether the skb has at least 2 bytes of tailroom, triggering
skb_over_panic when skb_tailroom(skb) < 2:

  skbuff: skb_over_panic: text:ffffffffc080071a len:386 put:2
  kernel BUG at net/core/skbuff.c:214!
  Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
  RIP: 0010:skb_panic+0x170/0x172
  Call Trace:
   <TASK>
   skb_put.cold+0x23/0x23
   cc2520_tx.constprop.0.isra.0+0x8a/0x1d0

Ensure at least 2 bytes of tailroom via pskb_expand_head() before calling
skb_put(skb, 2).

Tested in QEMU with KASAN enabled by passing a zero-tailroom skb to
cc2520_tx() with promiscuous mode enabled.

Fixes: 59869ebfe7a7 ("ieee802154: cc2520: Check CRC & add promiscuous")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Hui Peng <redacted>
---
Changes in v2:
- Split the cc2520 and mcr20a fixes into four single-issue patches
  (1/4..4/4) and documented each change in its own commit message as
  requested by Miquel Raynal.

 drivers/net/ieee802154/cc2520.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ieee802154/cc2520.c b/drivers/net/ieee802154/cc2520.c
index abfcfe0..5454872 100644
--- a/drivers/net/ieee802154/cc2520.c
+++ b/drivers/net/ieee802154/cc2520.c

@@ -482,8 +482,14 @@ cc2520_tx(struct ieee802154_hw *hw, struct sk_buff *skb)
 	 * values on RX. This means we need to manually add the CRC on TX.
 	 */
 	if (priv->promiscuous) {
-		u16 crc = crc_ccitt(0, skb->data, skb->len);
+		u16 crc;
 
+		if (skb_tailroom(skb) < 2 &&
+		    pskb_expand_head(skb, 0, 2, GFP_KERNEL)) {
+			rc = -ENOMEM;
+			goto err_tx;
+		}
+		crc = crc_ccitt(0, skb->data, skb->len);
 		put_unaligned_le16(crc, skb_put(skb, 2));
 		pkt_len = skb->len;
 	} else {

-- 
2.47.3