[PATCH 1/3] net: arc_emac: fix koops caused by sk_buff free

From: Alexander Kochetkov
Date: Tue Feb 09 2016 - 10:21:17 EST

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@xxxxxxxxx>

---
CC: stable@xxxxxxxxxxxxxxx # 3.18.x-
---
drivers/net/ethernet/arc/emac_main.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/arc/emac_main.c b/drivers/net/ethernet/arc/emac_main.c
index abe1eab..63a63e3 100644
--- a/drivers/net/ethernet/arc/emac_main.c
+++ b/drivers/net/ethernet/arc/emac_main.c
@@ -163,7 +163,7 @@ static void arc_emac_tx_clean(struct net_device *ndev)
struct sk_buff *skb = tx_buff->skb;
unsigned int info = le32_to_cpu(txbd->info);

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

if (unlikely(info & (DROP | DEFR | LTCL | UFLO))) {
@@ -191,6 +191,7 @@ static void arc_emac_tx_clean(struct net_device *ndev)

txbd->data = 0;
txbd->info = 0;
+ tx_buff->skb = NULL;

*txbd_dirty = (*txbd_dirty + 1) % TX_BD_NUM;
}
@@ -610,7 +611,6 @@ static int arc_emac_tx(struct sk_buff *skb, struct net_device *ndev)
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 */
@@ -620,6 +620,11 @@ static int arc_emac_tx(struct sk_buff *skb, struct net_device *ndev)

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

+ /* Make sure info word is set */
+ wmb();
+
+ priv->tx_buff[*txbd_curr].skb = skb;
+
/* Increment index to point to the next BD */
*txbd_curr = (*txbd_curr + 1) % TX_BD_NUM;

--
1.7.9.5