[PATCH 5.15 531/570] nfc: pn533: allocate rx skb before consuming bytes

Greg Kroah-Hartman
2026-04-13T16:40:55Z

From: Pengpeng Hou <pengpeng@iscas.ac.cn>

commit c71ba669b570c7b3f86ec875be222ea11dacb352 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/nfc/pn533/uart.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

--- a/drivers/nfc/pn533/uart.c
+++ b/drivers/nfc/pn533/uart.c
@@ -211,6 +211,13 @@ static int pn532_receive_buf(struct serd

del_timer(&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 int pn532_receive_buf(struct serd
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;