From bdf5d13aa05ec314d4385b31ac974d6c7e0997c9 Mon Sep 17 00:00:00 2001
From: Nick Child <nnac123@linux.ibm.com>
Date: Fri, 14 Feb 2025 09:52:33 -0600
Subject: [PATCH] ibmvnic: Don't reference skb after sending to VIOS
Previously, after successfully flushing the xmit buffer to VIOS,
the tx_bytes stat was incremented by the length of the skb.
It is invalid to access the skb memory after sending the buffer to
the VIOS because, at any point after sending, the VIOS can trigger
an interrupt to free this memory. A race between reading skb->len
and freeing the skb is possible (especially during LPM) and will
result in use-after-free:
==================================================================
BUG: KASAN: slab-use-after-free in ibmvnic_xmit+0x75c/0x1808 [ibmvnic]
Read of size 4 at addr c00000024eb48a70 by task hxecom/14495
<...>
Call Trace:
[c000000118f66cf0] [c0000000018cba6c] dump_stack_lvl+0x84/0xe8 (unreliable)
[c000000118f66d20] [c0000000006f0080] print_report+0x1a8/0x7f0
[c000000118f66df0] [c0000000006f08f0] kasan_report+0x128/0x1f8
[c000000118f66f00] [c0000000006f2868] __asan_load4+0xac/0xe0
[c000000118f66f20] [c0080000046eac84] ibmvnic_xmit+0x75c/0x1808 [ibmvnic]
[c000000118f67340] [c0000000014be168] dev_hard_start_xmit+0x150/0x358
<...>
Freed by task 0:
kasan_save_stack+0x34/0x68
kasan_save_track+0x2c/0x50
kasan_save_free_info+0x64/0x108
__kasan_mempool_poison_object+0x148/0x2d4
napi_skb_cache_put+0x5c/0x194
net_tx_action+0x154/0x5b8
handle_softirqs+0x20c/0x60c
do_softirq_own_stack+0x6c/0x88
<...>
The buggy address belongs to the object at c00000024eb48a00 which
belongs to the cache skbuff_head_cache of size 224
==================================================================
Fixes: 032c5e82847a ("Driver for IBM System i/p VNIC protocol")
Signed-off-by: Nick Child <nnac123@linux.ibm.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250214155233.235559-1-nnac123@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
drivers/net/ethernet/ibm/ibmvnic.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
index e95ae0d39948..0676fc547b6f 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -2408,6 +2408,7 @@ static netdev_tx_t ibmvnic_xmit(struct sk_buff *skb, struct net_device *netdev)
dma_addr_t data_dma_addr;
struct netdev_queue *txq;
unsigned long lpar_rc;
+ unsigned int skblen;
union sub_crq tx_crq;
unsigned int offset;
bool use_scrq_send_direct = false;
@@ -2522,6 +2523,7 @@ static netdev_tx_t ibmvnic_xmit(struct sk_buff *skb, struct net_device *netdev)
tx_buff->skb = skb;
tx_buff->index = bufidx;
tx_buff->pool_index = queue_num;
+ skblen = skb->len;
memset(&tx_crq, 0, sizeof(tx_crq));
tx_crq.v1.first = IBMVNIC_CRQ_CMD;
@@ -2614,7 +2616,7 @@ early_exit:
netif_stop_subqueue(netdev, queue_num);
}
- tx_bytes += skb->len;
+ tx_bytes += skblen;
txq_trans_cond_update(txq);
ret = NETDEV_TX_OK;
goto out;