[PATCH 6.6 038/166] nfc: s3fwrn5: allocate rx skb before consuming bytes

Greg Kroah-Hartman
2026-04-24T13:35:06Z

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

[ Upstream commit 5c14a19d5b1645cce1cb1252833d70b23635b632 ]

s3fwrn82_uart_read() reports the number of accepted bytes to the serdev
core. The current code consumes bytes into recv_skb and may already
deliver a complete 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: 3f52c2cb7e3a ("nfc: s3fwrn5: Support a UART interface")
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Link: https://patch.msgid.link/20260402042148.65236-1-pengpeng@iscas.ac.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/nfc/s3fwrn5/uart.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/nfc/s3fwrn5/uart.c b/drivers/nfc/s3fwrn5/uart.c
index 82ea35d748a5d..dde1a87ed1e47 100644
--- a/drivers/nfc/s3fwrn5/uart.c
+++ b/drivers/nfc/s3fwrn5/uart.c
@@ -59,6 +59,12 @@ static int s3fwrn82_uart_read(struct serdev_device *serdev,
size_t i;

for (i = 0; i < count; i++) {
+ if (!phy->recv_skb) {
+ phy->recv_skb = alloc_skb(NCI_SKB_BUFF_LEN, GFP_KERNEL);
+ if (!phy->recv_skb)
+ return i;
+ }
+
skb_put_u8(phy->recv_skb, *data++);

if (phy->recv_skb->len < S3FWRN82_NCI_HEADER)
@@ -70,9 +76,7 @@ static int s3fwrn82_uart_read(struct serdev_device *serdev,

s3fwrn5_recv_frame(phy->common.ndev, phy->recv_skb,
phy->common.mode);
- phy->recv_skb = alloc_skb(NCI_SKB_BUFF_LEN, GFP_KERNEL);
- if (!phy->recv_skb)
- return 0;
+ phy->recv_skb = NULL;
}

return i;
--
2.53.0