linux-kernel - [PATCH] Fix invalid-free in bcsp

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Date:   Fri,  1 Nov 2019 21:42:44 +0100
From:   Tomas Bortoli <tomasbortoli@...il.com>
To:     marcel@...tmann.org, johan.hedberg@...il.com
Cc:     linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller@...glegroups.com, Tomas Bortoli <tomasbortoli@...il.com>,
        syzbot+a0d209a4676664613e76@...kaller.appspotmail.com
Subject: [PATCH] Fix invalid-free in bcsp_close()

Syzbot reported an invalid-free that I introduced fixing a memleak.

bcsp_recv() also frees bcsp->rx_skb but never nullifies its value.
Nullify bcsp->rx_skb every time it is freed.

Signed-off-by: Tomas Bortoli <tomasbortoli@...il.com>
Reported-by: syzbot+a0d209a4676664613e76@...kaller.appspotmail.com
---
 drivers/bluetooth/hci_bcsp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/bluetooth/hci_bcsp.c b/drivers/bluetooth/hci_bcsp.c
index fe2e307009f4..cf4a56095817 100644
--- a/drivers/bluetooth/hci_bcsp.c
+++ b/drivers/bluetooth/hci_bcsp.c
@@ -591,6 +591,7 @@ static int bcsp_recv(struct hci_uart *hu, const void *data, int count)
 			if (*ptr == 0xc0) {
 				BT_ERR("Short BCSP packet");
 				kfree_skb(bcsp->rx_skb);
+				bcsp->rx_skb = NULL;
 				bcsp->rx_state = BCSP_W4_PKT_START;
 				bcsp->rx_count = 0;
 			} else
@@ -606,6 +607,7 @@ static int bcsp_recv(struct hci_uart *hu, const void *data, int count)
 			    bcsp->rx_skb->data[2])) != bcsp->rx_skb->data[3]) {
 				BT_ERR("Error in BCSP hdr checksum");
 				kfree_skb(bcsp->rx_skb);
+				bcsp->rx_skb = NULL;
 				bcsp->rx_state = BCSP_W4_PKT_DELIMITER;
 				bcsp->rx_count = 0;
 				continue;
@@ -630,6 +632,7 @@ static int bcsp_recv(struct hci_uart *hu, const void *data, int count)
 				       bscp_get_crc(bcsp));
 
 				kfree_skb(bcsp->rx_skb);
+				bcsp->rx_skb = NULL;
 				bcsp->rx_state = BCSP_W4_PKT_DELIMITER;
 				bcsp->rx_count = 0;
 				continue;
-- 
2.20.1