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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jia-Ju Bai <baijiaju1990@gmail.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.4 077/137] net: nfc: nci: fix a possible sleep-in-atomic-context bug in nci_uart_tty_receive()
Date:   Thu,  2 Jan 2020 23:07:30 +0100
Message-Id: <20200102220557.086899682@linuxfoundation.org>
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From: Jia-Ju Bai <baijiaju1990@gmail.com>

[ Upstream commit b7ac893652cafadcf669f78452329727e4e255cc ]

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@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/nfc/nci/uart.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/nfc/nci/uart.c
+++ b/net/nfc/nci/uart.c
@@ -355,7 +355,7 @@ static int nci_uart_default_recv_buf(str
 			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;
 		}