Commit message: net: arc_emac: fix koops caused by sk_buff free

There is a race between arc_emac_tx() and arc_emac_tx_clean().
sk_buff got freed by arc_emac_tx_clean() while arc_emac_tx()
submitting sk_buff.

In order to free sk_buff arc_emac_tx_clean() checks:
    if ((info & FOR_EMAC) || !txbd->data)
        break;
    ...
    dev_kfree_skb_irq(skb);

If condition false, arc_emac_tx_clean() free sk_buff.

In order to submit txbd, arc_emac_tx() do:
    priv->tx_buff[*txbd_curr].skb = skb;
    ...
    priv->txbd[*txbd_curr].data = cpu_to_le32(addr);
    ...
    ...  <== arc_emac_tx_clean() check condition here
    ...  <== (info & FOR_EMAC) is false
    ...  <== !txbd->data is false
    ...
    *info = cpu_to_le32(FOR_EMAC | FIRST_OR_LAST_MASK | len);

In order to reproduce the situation,
run device:
    # iperf -s
run on host:
    # iperf -t 600 -c <device-ip-addr>

[   28.396284] ------------[ cut here ]------------
[   28.400912] kernel BUG at .../net/core/skbuff.c:1355!
[   28.414019] Internal error: Oops - BUG: 0 [#1] SMP ARM
[   28.419150] Modules linked in:
[   28.422219] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G    B           4.4.0+ #120
[   28.429516] Hardware name: Rockchip (Device Tree)
[   28.434216] task: c0665070 ti: c0660000 task.ti: c0660000
[   28.439622] PC is at skb_put+0x10/0x54
[   28.443381] LR is at arc_emac_poll+0x260/0x474
[   28.447821] pc : [<c03af580>]    lr : [<c028fec4>]    psr: a0070113
[   28.447821] sp : c0661e58  ip : eea68502  fp : ef377000
[   28.459280] r10: 0000012c  r9 : f08b2000  r8 : eeb57100
[   28.464498] r7 : 00000000  r6 : ef376594  r5 : 00000077  r4 : ef376000
[   28.471015] r3 : 0030488b  r2 : ef13e880  r1 : 000005ee  r0 : eeb57100
[   28.477534] Flags: NzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
[   28.484658] Control: 10c5387d  Table: 8eaf004a  DAC: 00000051
[   28.490396] Process swapper/0 (pid: 0, stack limit = 0xc0660210)
[   28.496393] Stack: (0xc0661e58 to 0xc0662000)
[   28.500745] 1e40:                                                       00000002 00000000
[   28.508913] 1e60: 00000000 ef376520 00000028 f08b23b8 00000000 ef376520 ef7b6900 c028fc64
[   28.517082] 1e80: 2f158000 c0661ea8 c0661eb0 0000012c c065e900 c03bdeac ffff95e9 c0662100
[   28.525250] 1ea0: c0663924 00000028 c0661ea8 c0661ea8 c0661eb0 c0661eb0 0000001e c0660000
[   28.533417] 1ec0: 40000003 00000008 c0695a00 0000000a c066208c 00000100 c0661ee0 c0027410
[   28.541584] 1ee0: ef0fb700 2f158000 00200000 ffff95e8 00000004 c0662100 c0662080 00000003
[   28.549751] 1f00: 00000000 00000000 00000000 c065b45c 0000001e ef005000 c0647a30 00000000
[   28.557919] 1f20: 00000000 c0027798 00000000 c005cf40 f0802100 c0662ffc c0661f60 f0803100
[   28.566088] 1f40: c0661fb8 c00093bc c000ffb4 60070013 ffffffff c0661f94 c0661fb8 c00137d4
[   28.574267] 1f60: 00000001 00000000 00000000 c001ffa0 00000000 c0660000 00000000 c065a364
[   28.582441] 1f80: c0661fb8 c0647a30 00000000 00000000 00000000 c0661fb0 c000ffb0 c000ffb4
[   28.590608] 1fa0: 60070013 ffffffff 00000051 00000000 00000000 c005496c c0662400 c061bc40
[   28.598776] 1fc0: ffffffff ffffffff 00000000 c061b680 00000000 c0647a30 00000000 c0695294
[   28.606943] 1fe0: c0662488 c0647a2c c066619c 6000406a 413fc090 6000807c 00000000 00000000
[   28.615127] [<c03af580>] (skb_put) from [<ef376520>] (0xef376520)
[   28.621218] Code: e5902054 e590c090 e3520000 0a000000 (e7f001f2)
[   28.627307] ---[ end trace 4824734e2243fdb6 ]---

[   34.377068] Internal error: Oops: 17 [#1] SMP ARM
[   34.382854] Modules linked in:
[   34.385947] CPU: 0 PID: 3 Comm: ksoftirqd/0 Not tainted 4.4.0+ #120
[   34.392219] Hardware name: Rockchip (Device Tree)
[   34.396937] task: ef02d040 ti: ef05c000 task.ti: ef05c000
[   34.402376] PC is at __dev_kfree_skb_irq+0x4/0x80
[   34.407121] LR is at arc_emac_poll+0x130/0x474
[   34.411583] pc : [<c03bb640>]    lr : [<c028fd94>]    psr: 60030013
[   34.411583] sp : ef05de68  ip : 0008e83c  fp : ef377000
[   34.423062] r10: c001bec4  r9 : 00000000  r8 : f08b24c8
[   34.428296] r7 : f08b2400  r6 : 00000075  r5 : 00000019  r4 : ef376000
[   34.434827] r3 : 00060000  r2 : 00000042  r1 : 00000001  r0 : 00000000
[   34.441365] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
[   34.448507] Control: 10c5387d  Table: 8f25c04a  DAC: 00000051
[   34.454262] Process ksoftirqd/0 (pid: 3, stack limit = 0xef05c210)
[   34.460449] Stack: (0xef05de68 to 0xef05e000)
[   34.464827] de60:                   ef376000 c028fd94 00000000 c0669480 c0669480 ef376520
[   34.473022] de80: 00000028 00000001 00002ae4 ef376520 ef7b6900 c028fc64 2f158000 ef05dec0
[   34.481215] dea0: ef05dec8 0000012c c065e900 c03bdeac ffff983f c0662100 c0663924 00000028
[   34.489409] dec0: ef05dec0 ef05dec0 ef05dec8 ef05dec8 ef7b6000 ef05c000 40000003 00000008
[   34.497600] dee0: c0695a00 0000000a c066208c 00000100 ef05def8 c0027410 ef7b6000 40000000
[   34.505795] df00: 04208040 ffff983e 00000004 c0662100 c0662080 00000003 ef05c000 ef027340
[   34.513985] df20: ef05c000 c0666c2c 00000000 00000001 00000002 00000000 00000000 c0027568
[   34.522176] df40: ef027340 c003ef48 ef027300 00000000 ef027340 c003edd4 00000000 00000000
[   34.530367] df60: 00000000 c003c37c ffffff7f 00000001 00000000 ef027340 00000000 00030003
[   34.538559] df80: ef05df80 ef05df80 00000000 00000000 ef05df90 ef05df90 ef05dfac ef027300
[   34.546750] dfa0: c003c2a4 00000000 00000000 c000f578 00000000 00000000 00000000 00000000
[   34.554939] dfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[   34.563129] dfe0: 00000000 00000000 00000000 00000000 00000013 00000000 ffffffff dfff7fff
[   34.571360] [<c03bb640>] (__dev_kfree_skb_irq) from [<c028fd94>] (arc_emac_poll+0x130/0x474)
[   34.579840] [<c028fd94>] (arc_emac_poll) from [<c03bdeac>] (net_rx_action+0xdc/0x28c)
[   34.587712] [<c03bdeac>] (net_rx_action) from [<c0027410>] (__do_softirq+0xcc/0x1f8)
[   34.595482] [<c0027410>] (__do_softirq) from [<c0027568>] (run_ksoftirqd+0x2c/0x50)
[   34.603168] [<c0027568>] (run_ksoftirqd) from [<c003ef48>] (smpboot_thread_fn+0x174/0x18c)
[   34.611466] [<c003ef48>] (smpboot_thread_fn) from [<c003c37c>] (kthread+0xd8/0xec)
[   34.619075] [<c003c37c>] (kthread) from [<c000f578>] (ret_from_fork+0x14/0x3c)
[   34.626317] Code: e8bd8010 e3a00000 e12fff1e e92d4010 (e59030a4)
[   34.632572] ---[ end trace cca5a3d86a82249a ]---

Signed-off-by: Alexander Kochetkov <al.kochet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE: CVE-2016-10906
CWE: CWE-362
Vulnerability description: An issue was discovered in drivers/net/ethernet/arc/emac_main.c in the Linux kernel before 4.5. A use-after-free is caused by a race condition between the functions arc_emac_tx and arc_emac_tx_clean.

Project: linux
File: emac_main.c

static void arc_emac_tx_clean(struct net_device *ndev)
{
	struct arc_emac_priv *priv = netdev_priv(ndev);
	struct net_device_stats *stats = &ndev->stats;
	unsigned int i;

	for (i = 0; i < TX_BD_NUM; i++) {
		unsigned int *txbd_dirty = &priv->txbd_dirty;
		struct arc_emac_bd *txbd = &priv->txbd[*txbd_dirty];
		struct buffer_state *tx_buff = &priv->tx_buff[*txbd_dirty];
		struct sk_buff *skb = tx_buff->skb;
		unsigned int info = le32_to_cpu(txbd->info);

		if ((info & FOR_EMAC) || !txbd->data)
			break;

		if (unlikely(info & (DROP | DEFR | LTCL | UFLO))) {
			stats->tx_errors++;
			stats->tx_dropped++;

			if (info & DEFR)
				stats->tx_carrier_errors++;

			if (info & LTCL)
				stats->collisions++;

			if (info & UFLO)
				stats->tx_fifo_errors++;
		} else if (likely(info & FIRST_OR_LAST_MASK)) {
			stats->tx_packets++;
			stats->tx_bytes += skb->len;
		}

		dma_unmap_single(&ndev->dev, dma_unmap_addr(tx_buff, addr),
				 dma_unmap_len(tx_buff, len), DMA_TO_DEVICE);

		/* return the sk_buff to system */
		dev_kfree_skb_irq(skb);

		txbd->data = 0;
		txbd->info = 0;

		*txbd_dirty = (*txbd_dirty + 1) % TX_BD_NUM;
	}

	/* Ensure that txbd_dirty is visible to tx() before checking
	 * for queue stopped.
	 */
	smp_mb();

	if (netif_queue_stopped(ndev) && arc_emac_tx_avail(priv))
		netif_wake_queue(ndev);
}

Project: linux
File: emac_main.c

static int arc_emac_tx(struct sk_buff *skb, struct net_device *ndev)
{
	struct arc_emac_priv *priv = netdev_priv(ndev);
	unsigned int len, *txbd_curr = &priv->txbd_curr;
	struct net_device_stats *stats = &ndev->stats;
	__le32 *info = &priv->txbd[*txbd_curr].info;
	dma_addr_t addr;

	if (skb_padto(skb, ETH_ZLEN))
		return NETDEV_TX_OK;

	len = max_t(unsigned int, ETH_ZLEN, skb->len);

	if (unlikely(!arc_emac_tx_avail(priv))) {
		netif_stop_queue(ndev);
		netdev_err(ndev, "BUG! Tx Ring full when queue awake!\n");
		return NETDEV_TX_BUSY;
	}

	addr = dma_map_single(&ndev->dev, (void *)skb->data, len,
			      DMA_TO_DEVICE);

	if (unlikely(dma_mapping_error(&ndev->dev, addr))) {
		stats->tx_dropped++;
		stats->tx_errors++;
		dev_kfree_skb(skb);
		return NETDEV_TX_OK;
	}
	dma_unmap_addr_set(&priv->tx_buff[*txbd_curr], addr, addr);
	dma_unmap_len_set(&priv->tx_buff[*txbd_curr], len, len);

	priv->tx_buff[*txbd_curr].skb = skb;
	priv->txbd[*txbd_curr].data = cpu_to_le32(addr);

	/* Make sure pointer to data buffer is set */
	wmb();

	skb_tx_timestamp(skb);

	*info = cpu_to_le32(FOR_EMAC | FIRST_OR_LAST_MASK | len);

	/* Increment index to point to the next BD */
	*txbd_curr = (*txbd_curr + 1) % TX_BD_NUM;

	/* Ensure that tx_clean() sees the new txbd_curr before
	 * checking the queue status. This prevents an unneeded wake
	 * of the queue in tx_clean().
	 */
	smp_mb();

	if (!arc_emac_tx_avail(priv)) {
		netif_stop_queue(ndev);
		/* Refresh tx_dirty */
		smp_mb();
		if (arc_emac_tx_avail(priv))
			netif_start_queue(ndev);
	}

	arc_reg_set(priv, R_STATUS, TXPL_MASK);

	return NETDEV_TX_OK;
}