bpf: Fix NULL deref in __list_del_clearprev for flush_node

[kernel-patches-daemon-bpf]

Pull request for series with
subject: bpf: Fix NULL deref in __list_del_clearprev for flush_node
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1033576

[kernel-patches-daemon-bpf]

Upstream branch: 6f0b824
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1033576
version: 1

[kernel-patches-review-bot]

commit 120974cc28b023d86af8b1f0e0cf8b8c0ed7e575
Author: DLpang <[email protected]>

bpf: Fix NULL deref in __list_del_clearprev for flush_node

This patch fixes a NULL pointer dereference in the BPF subsystem by
adding initialization and defensive checks for the flush_node list_head
in per-CPU XDP bulk queues.

Link: https://syzkaller.appspot.com/bug?extid=2b3391f44313b3983e91

> diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> index 04171fbc39cb..6ab6eae31989 100644
> --- a/kernel/bpf/cpumap.c
> +++ b/kernel/bpf/cpumap.c
> @@ -450,6 +450,7 @@ __cpu_map_entry_alloc(struct bpf_map *map, struct bpf_cpumap_val *value,
>
>  	for_each_possible_cpu(i) {
>  		bq = per_cpu_ptr(rcpu->bulkq, i);
> +		INIT_LIST_HEAD(&bq->flush_node);
>  		bq->obj = rcpu;
>  	}
>

[ ... ]

> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index 2625601de76e..7a7347e709cc 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
> @@ -428,7 +428,8 @@ void __dev_flush(struct list_head *flush_list)
>  		bq_xmit_all(bq, XDP_XMIT_FLUSH);
>  		bq->dev_rx = NULL;
>  		bq->xdp_prog = NULL;
> -		__list_del_clearprev(&bq->flush_node);
> +		if (bq->flush_node.prev)
> +			__list_del_clearprev(&bq->flush_node);
                ^^^^

The devmap code adds the same defensive check but doesn't initialize
flush_node the way cpumap does. Looking at dev_map_notification(), when
NETDEV_REGISTER occurs, it calls:

    alloc_percpu(struct xdp_dev_bulk_queue)

And then only initializes the dev field:

    per_cpu_ptr(netdev->xdp_bulkq, cpu)->dev = netdev;

Without INIT_LIST_HEAD(&bq->flush_node), if alloc_percpu() returns
memory with non-zero bytes, bq->flush_node.prev could contain garbage.

The enqueue path in bq_enqueue() uses:

    if (!bq->dev_rx)
        list_add(&bq->flush_node, flush_list);

So if dev_rx contains non-zero garbage, the node never gets added to the
list. But this flush code checks bq->flush_node.prev which could also be
garbage, causing __list_del_clearprev() to be called with invalid
pointers.

Does devmap need INIT_LIST_HEAD(&bq->flush_node) similar to cpumap? The
commit message states that initialization is part of the fix, but only
cpumap gets it.

[ ... ]

---

AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

In-Reply-To-Subject: bpf: Fix NULL deref in __list_del_clearprev for flush_node
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/20255377282

[kernel-patches-daemon-bpf]

Forwarding comment 3658573525 via email
In-Reply-To: [email protected]
Patch: https://patchwork.kernel.org/project/netdevbpf/patch/[email protected]/

[kernel-patches-daemon-bpf]

Upstream branch: 6f0b824
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1033576
version: 1

[kernel-patches-daemon-bpf]

At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=1033576 expired. Closing PR.