[PATCH AUTOSEL 5.10 15/54] gianfar: fix jumbo packets+napi+rx overrun crash

Sasha Levin
2021-03-17T00:59:14Z

From: Michael Braun <michael-dev@fami-braun.de>

[ Upstream commit d8861bab48b6c1fc3cdbcab8ff9d1eaea43afe7f ]

When using jumbo packets and overrunning rx queue with napi enabled,
the following sequence is observed in gfar_add_rx_frag:

| lstatus | | skb |
t | lstatus, size, flags | first | len, data_len, *ptr |
---+--------------------------------------+-------+-----------------------+
13 | 18002348, 9032, INTERRUPT LAST | 0 | 9600, 8000, f554c12e |
12 | 10000640, 1600, INTERRUPT | 0 | 8000, 6400, f554c12e |
11 | 10000640, 1600, INTERRUPT | 0 | 6400, 4800, f554c12e |
10 | 10000640, 1600, INTERRUPT | 0 | 4800, 3200, f554c12e |
09 | 10000640, 1600, INTERRUPT | 0 | 3200, 1600, f554c12e |
08 | 14000640, 1600, INTERRUPT FIRST | 0 | 1600, 0, f554c12e |
07 | 14000640, 1600, INTERRUPT FIRST | 1 | 0, 0, f554c12e |
06 | 1c000080, 128, INTERRUPT LAST FIRST | 1 | 0, 0, abf3bd6e |
05 | 18002348, 9032, INTERRUPT LAST | 0 | 8000, 6400, c5a57780 |
04 | 10000640, 1600, INTERRUPT | 0 | 6400, 4800, c5a57780 |
03 | 10000640, 1600, INTERRUPT | 0 | 4800, 3200, c5a57780 |
02 | 10000640, 1600, INTERRUPT | 0 | 3200, 1600, c5a57780 |
01 | 10000640, 1600, INTERRUPT | 0 | 1600, 0, c5a57780 |
00 | 14000640, 1600, INTERRUPT FIRST | 1 | 0, 0, c5a57780 |

So at t=7 a new packets is started but not finished, probably due to rx
overrun - but rx overrun is not indicated in the flags. Instead a new
packets starts at t=8. This results in skb->len to exceed size for the LAST
fragment at t=13 and thus a negative fragment size added to the skb.

This then crashes:

kernel BUG at include/linux/skbuff.h:2277!
Oops: Exception in kernel mode, sig: 5 [#1]
...
NIP [c04689f4] skb_pull+0x2c/0x48
LR [c03f62ac] gfar_clean_rx_ring+0x2e4/0x844
Call Trace:
[ec4bfd38] [c06a84c4] _raw_spin_unlock_irqrestore+0x60/0x7c (unreliable)
[ec4bfda8] [c03f6a44] gfar_poll_rx_sq+0x48/0xe4
[ec4bfdc8] [c048d504] __napi_poll+0x54/0x26c
[ec4bfdf8] [c048d908] net_rx_action+0x138/0x2c0
[ec4bfe68] [c06a8f34] __do_softirq+0x3a4/0x4fc
[ec4bfed8] [c0040150] run_ksoftirqd+0x58/0x70
[ec4bfee8] [c0066ecc] smpboot_thread_fn+0x184/0x1cc
[ec4bff08] [c0062718] kthread+0x140/0x144
[ec4bff38] [c0012350] ret_from_kernel_thread+0x14/0x1c

This patch fixes this by checking for computed LAST fragment size, so a
negative sized fragment is never added.
In order to prevent the newer rx frame from getting corrupted, the FIRST
flag is checked to discard the incomplete older frame.

Signed-off-by: Michael Braun <michael-dev@fami-braun.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/ethernet/freescale/gianfar.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)

diff --git a/drivers/net/ethernet/freescale/gianfar.c b/drivers/net/ethernet/freescale/gianfar.c
index d391a45cebb6..4fab2ee5bbf5 100644
--- a/drivers/net/ethernet/freescale/gianfar.c
+++ b/drivers/net/ethernet/freescale/gianfar.c
@@ -2391,6 +2391,10 @@ static bool gfar_add_rx_frag(struct gfar_rx_buff *rxb, u32 lstatus,
if (lstatus & BD_LFLAG(RXBD_LAST))
size -= skb->len;

+ WARN(size < 0, "gianfar: rx fragment size underflow");
+ if (size < 0)
+ return false;
+
skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, page,
rxb->page_offset + RXBUF_ALIGNMENT,
size, GFAR_RXB_TRUESIZE);
@@ -2553,6 +2557,17 @@ static int gfar_clean_rx_ring(struct gfar_priv_rx_q *rx_queue,
if (lstatus & BD_LFLAG(RXBD_EMPTY))
break;

+ /* lost RXBD_LAST descriptor due to overrun */
+ if (skb &&
+ (lstatus & BD_LFLAG(RXBD_FIRST))) {
+ /* discard faulty buffer */
+ dev_kfree_skb(skb);
+ skb = NULL;
+ rx_queue->stats.rx_dropped++;
+
+ /* can continue normally */
+ }
+
/* order rx buffer descriptor reads */
rmb();

--
2.30.1