netdev - [PATCH v2] iwl4965: Fix a null pointer dereference in il_tx_queue_free and il_cmd_queue

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Message-Id: <1452519775-7049-1-git-send-email-baijiaju1990@163.com>
Date:	Mon, 11 Jan 2016 21:42:54 +0800
From:	Jia-Ju Bai <baijiaju1990@....com>
To:	sgruszka@...hat.com, kvalo@...eaurora.org, johannes.berg@...el.com,
	emmanuel.grumbach@...el.com
Cc:	ilw@...ux.intel.com, linuxwifi@...el.com,
	linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
	Jia-Ju Bai <baijiaju1990@....com>
Subject: [PATCH v2] iwl4965: Fix a null pointer dereference in il_tx_queue_free and il_cmd_queue_free

If "txq->cmd = kzalloc(...)" in il_tx_queue_init fails,
"kfree(txq->cmd[i])" in il_tx_queue_free and il_cmd_queue_free
in iwl4965_hw_txq_ctx_free will causes a null pointer dereference,
because txq->cmd is NULL at that time.

This patch fixes this problem by adding a if-check before kfree.
To avoid double free in il_tx_queue_free and il_cmd_queue_free
caused by the fixing, txq->meta and txq->cmd in error handling code
of il_tx_queue_init are assigned null values. 
Otherwise, a double free will occur.

This patch has been tested in real device, and it actually fixes the bug.
Thanks Stanislaw for his suggestion.

Signed-off-by: Jia-Ju Bai <baijiaju1990@....com>
---
 drivers/net/wireless/iwlegacy/common.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wireless/iwlegacy/common.c b/drivers/net/wireless/iwlegacy/common.c
index 8871145..092ecbc 100644
--- a/drivers/net/wireless/iwlegacy/common.c
+++ b/drivers/net/wireless/iwlegacy/common.c
@@ -2794,8 +2794,10 @@ il_tx_queue_free(struct il_priv *il, int txq_id)
 	il_tx_queue_unmap(il, txq_id);
 
 	/* De-alloc array of command/tx buffers */
-	for (i = 0; i < TFD_TX_CMD_SLOTS; i++)
-		kfree(txq->cmd[i]);
+	if (txq->cmd) {
+		for (i = 0; i < TFD_TX_CMD_SLOTS; i++)
+			kfree(txq->cmd[i]);
+	}
 
 	/* De-alloc circular buffer of TFDs */
 	if (txq->q.n_bd)
@@ -2873,8 +2875,10 @@ il_cmd_queue_free(struct il_priv *il)
 	il_cmd_queue_unmap(il);
 
 	/* De-alloc array of command/tx buffers */
-	for (i = 0; i <= TFD_CMD_SLOTS; i++)
-		kfree(txq->cmd[i]);
+	if (txq->cmd) {
+		for (i = 0; i <= TFD_CMD_SLOTS; i++)
+			kfree(txq->cmd[i]);
+	}
 
 	/* De-alloc circular buffer of TFDs */
 	if (txq->q.n_bd)
@@ -3080,7 +3084,9 @@ err:
 		kfree(txq->cmd[i]);
 out_free_arrays:
 	kfree(txq->meta);
+	txq->meta = NULL;
 	kfree(txq->cmd);
+	txq->cmd = NULL;
 
 	return -ENOMEM;
 }
-- 
1.7.9.5