nfc: pn533: allocate rx skb before consuming bytes

pn532_receive_buf() reports the number of accepted bytes to the serdev
core. The current code consumes bytes into recv_skb and may already hand
a complete frame to pn533_recv_frame() before allocating a fresh receive
buffer.

If that alloc_skb() fails, the callback returns 0 even though it has
already consumed bytes, and it leaves recv_skb as NULL for the next
receive callback. That breaks the receive_buf() accounting contract and
can also lead to a NULL dereference on the next skb_put_u8().

Allocate the receive skb lazily before consuming the next byte instead.
If allocation fails, return the number of bytes already accepted.

Fixes: c656aa4c27b1 ("nfc: pn533: add UART phy driver")
Cc: stable@vger.kernel.org
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Link: https://patch.msgid.link/20260405094003.3-pn533-v2-pengpeng@iscas.ac.cn
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/drivers/nfc/pn533/uart.c b/drivers/nfc/pn533/uart.c
index 1b82b7b2a5fae81fd372ff223bdbed43161914e5..e0d67cd2ac9b8f76b407cdc59d3b7f73e6900f8b 100644 (file)
--- a/drivers/nfc/pn533/uart.c
+++ b/drivers/nfc/pn533/uart.c
@@ -211,6 +211,13 @@ static size_t pn532_receive_buf(struct serdev_device *serdev,
 
        timer_delete(&dev->cmd_timeout);
        for (i = 0; i < count; i++) {
+               if (!dev->recv_skb) {
+                       dev->recv_skb = alloc_skb(PN532_UART_SKB_BUFF_LEN,
+                                                 GFP_KERNEL);
+                       if (!dev->recv_skb)
+                               return i;
+               }
+
                if (unlikely(!skb_tailroom(dev->recv_skb)))
                        skb_trim(dev->recv_skb, 0);
 
@@ -219,9 +226,7 @@ static size_t pn532_receive_buf(struct serdev_device *serdev,
                        continue;
 
                pn533_recv_frame(dev->priv, dev->recv_skb, 0);
-               dev->recv_skb = alloc_skb(PN532_UART_SKB_BUFF_LEN, GFP_KERNEL);
-               if (!dev->recv_skb)
-                       return 0;
+               dev->recv_skb = NULL;
        }
 
        return i;