[PATCH] net: nfc: nci: fix a possible sleep-in-atomic-context bug in nci_uart_tty_receive()

[Jia-Ju Bai]

The kernel may sleep while holding a spinlock.
The function call path (from bottom to top) in Linux 4.19 is:

net/nfc/nci/uart.c, 349: 
	nci_skb_alloc in nci_uart_default_recv_buf
net/nfc/nci/uart.c, 255: 
	(FUNC_PTR)nci_uart_default_recv_buf in nci_uart_tty_receive
net/nfc/nci/uart.c, 254: 
	spin_lock in nci_uart_tty_receive

nci_skb_alloc(GFP_KERNEL) can sleep at runtime.
(FUNC_PTR) means a function pointer is called.

To fix this bug, GFP_KERNEL is replaced with GFP_ATOMIC for
nci_skb_alloc().

This bug is found by a static analysis tool STCheck written by myself.

Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
---
 net/nfc/nci/uart.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/nfc/nci/uart.c b/net/nfc/nci/uart.c
index 78fe622eba65..11b554ce07ff 100644
--- a/net/nfc/nci/uart.c
+++ b/net/nfc/nci/uart.c
@@ -346,7 +346,7 @@ static int nci_uart_default_recv_buf(struct nci_uart *nu, const u8 *data,
 			nu->rx_packet_len = -1;
 			nu->rx_skb = nci_skb_alloc(nu->ndev,
 						   NCI_MAX_PACKET_SIZE,
-						   GFP_KERNEL);
+						   GFP_ATOMIC);
 			if (!nu->rx_skb)
 				return -ENOMEM;
 		}
-- 
2.17.1