[PATCH] atlantic: fix double-free in aq_ring_tx_clean

We found this bug while fuzzing the device driver. Using and freeing
the dangling pointer buff->skb would cause use-after-free and
double-free.

This bug is triggerable with compromised/malfunctioning devices. We
found the bug with QEMU emulation and tested the patch by emulation.
We did NOT test on a real device.

Attached is the bug report.

BUG: KASAN: double-free or invalid-free in consume_skb+0x6c/0x1c0

Call Trace:
 dump_stack+0x76/0xa0
 print_address_description.constprop.0+0x16/0x200
 ? consume_skb+0x6c/0x1c0
 kasan_report_invalid_free+0x61/0xa0
 ? consume_skb+0x6c/0x1c0
 __kasan_slab_free+0x15e/0x170
 ? consume_skb+0x6c/0x1c0
 kfree+0x8c/0x230
 consume_skb+0x6c/0x1c0
 aq_ring_tx_clean+0x5c2/0xa80 [atlantic]
 aq_vec_poll+0x309/0x5d0 [atlantic]
 ? _sub_I_65535_1+0x20/0x20 [atlantic]
 ? __next_timer_interrupt+0xba/0xf0
 net_rx_action+0x363/0xbd0
 ? call_timer_fn+0x240/0x240
 ? __switch_to_asm+0x34/0x70
 ? napi_busy_loop+0x520/0x520
 ? net_tx_action+0x379/0x720
 __do_softirq+0x18c/0x634
 ? takeover_tasklets+0x5f0/0x5f0
 run_ksoftirqd+0x15/0x20
 smpboot_thread_fn+0x2f1/0x6b0
 ? smpboot_unregister_percpu_thread+0x160/0x160
 ? __kthread_parkme+0x80/0x100
 ? smpboot_unregister_percpu_thread+0x160/0x160
 kthread+0x2b5/0x3b0
 ? kthread_create_on_node+0xd0/0xd0
 ret_from_fork+0x22/0x40

Reported-by: Brendan Dolan-Gavitt <redacted>
Signed-off-by: Zekun Shen <redacted>
---
 drivers/net/ethernet/aquantia/atlantic/aq_ring.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/aquantia/atlantic/aq_ring.c b/drivers/net/ethernet/aquantia/atlantic/aq_ring.c
index 24122ccda614..81b3756417ec 100644
--- a/drivers/net/ethernet/aquantia/atlantic/aq_ring.c
+++ b/drivers/net/ethernet/aquantia/atlantic/aq_ring.c

@@ -298,13 +298,14 @@ bool aq_ring_tx_clean(struct aq_ring_s *self)
 			}
 		}
 
-		if (unlikely(buff->is_eop)) {
+		if (unlikely(buff->is_eop && buff->skb)) {
 			u64_stats_update_begin(&self->stats.tx.syncp);
 			++self->stats.tx.packets;
 			self->stats.tx.bytes += buff->skb->len;
 			u64_stats_update_end(&self->stats.tx.syncp);
 
 			dev_kfree_skb_any(buff->skb);
+			buff->skb = NULL;
 		}
 		buff->pa = 0U;
 		buff->eop_index = 0xffffU;

-- 
2.25.1

We found this bug while fuzzing the device driver. Using and freeing
the dangling pointer buff->skb would cause use-after-free and
double-free.

This bug is triggerable with compromised/malfunctioning devices. We
found the bug with QEMU emulation and tested the patch by emulation.
We did NOT test on a real device.

Attached is the bug report.

Reviewed-by: Igor Russkikh <redacted>

Thank you for submitting this!

Igor

Hello:

This patch was applied to netdev/net.git (master)
by David S. Miller [off-list ref]:

On Thu, 18 Nov 2021 16:08:02 -0500 you wrote:

We found this bug while fuzzing the device driver. Using and freeing
the dangling pointer buff->skb would cause use-after-free and
double-free.

This bug is triggerable with compromised/malfunctioning devices. We
found the bug with QEMU emulation and tested the patch by emulation.
We did NOT test on a real device.

[...]

Here is the summary with links:
  - atlantic: fix double-free in aq_ring_tx_clean
    https://git.kernel.org/netdev/net/c/6a405f6c372d

You are awesome, thank you!
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