netdev - Re: [PATCH bpf-next v4 01/16] bpf: Select bpf_local_storage_map_bucket based on bpf_local

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <fc5f36c2f50b99cba8b9b6d020a7400911a84c372ca15be7707c8513239228f3@mail.kernel.org>
Date: Sat, 31 Jan 2026 05:33:32 +0000 (UTC)
From: bot+bpf-ci@...nel.org
To: ameryhung@...il.com,bpf@...r.kernel.org
Cc: netdev@...r.kernel.org,alexei.starovoitov@...il.com,andrii@...nel.org,daniel@...earbox.net,memxor@...il.com,martin.lau@...nel.org,kpsingh@...nel.org,yonghong.song@...ux.dev,song@...nel.org,haoluo@...gle.com,ameryhung@...il.com,kernel-team@...a.com,ast@...nel.org,andrii@...nel.org,daniel@...earbox.net,martin.lau@...nel.org,eddyz87@...il.com,yonghong.song@...ux.dev,clm@...a.com,ihor.solodrai@...ux.dev
Subject: Re: [PATCH bpf-next v4 01/16] bpf: Select bpf_local_storage_map_bucket based on bpf_local_storage

> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
> index e2fe6c328..6615091dd 100644
> --- a/kernel/bpf/bpf_local_storage.c
> +++ b/kernel/bpf/bpf_local_storage.c

[ ... ]

> @@ -368,9 +371,13 @@ static void bpf_selem_unlink_map(struct bpf_local_storage_elem *selem)
>  void bpf_selem_link_map(struct bpf_local_storage_map *smap,
>  			struct bpf_local_storage_elem *selem)
>  {
> -	struct bpf_local_storage_map_bucket *b = select_bucket(smap, selem);
> +	struct bpf_local_storage *local_storage;
> +	struct bpf_local_storage_map_bucket *b;
>  	unsigned long flags;
>
> +	local_storage = rcu_dereference_check(selem->local_storage,
> +					      bpf_rcu_lock_held());
> +	b = select_bucket(smap, local_storage);

The commit message states: "This is safe since a selem is always linked to
local_storage before linked to map."

Is this claim accurate? Looking at bpf_local_storage_update(), the order is:

    /* First, link the new selem to the map */
    bpf_selem_link_map(smap, selem);

    /* Second, link (and publish) the new selem to local_storage */
    bpf_selem_link_storage_nolock(local_storage, selem);

The comment explicitly says "First, link the new selem to the map" which is
the opposite order from what the commit message claims.

Similarly, in bpf_sk_storage_clone() when new_sk_storage is non-NULL:

    bpf_selem_link_map(smap, copy_selem);
    bpf_selem_link_storage_nolock(new_sk_storage, copy_selem);

Since bpf_selem_alloc() does not initialize selem->local_storage (it only
sets SDATA(selem)->smap), and bpf_selem_link_storage_nolock() is what sets
selem->local_storage, wouldn't this mean bpf_selem_link_map() reads NULL
from selem->local_storage?

With local_storage being NULL, select_bucket() would compute hash_ptr(NULL)
which returns 0, placing all newly linked selems into bucket 0. Later when
bpf_selem_unlink_map() runs, selem->local_storage has been set, so it
computes a different bucket and tries to unlink from the wrong bucket.

The next commit in the series (82de4fd08 "bpf: Convert bpf_selem_unlink_map
to failable") introduces bpf_selem_link_map_nolock() to fix this for
bpf_local_storage_alloc() and bpf_local_storage_update(), but
bpf_sk_storage_clone() still uses bpf_selem_link_map() and appears to
remain affected throughout the series.

>  	raw_spin_lock_irqsave(&b->lock, flags);
>  	hlist_add_head_rcu(&selem->map_node, &b->list);
>  	raw_spin_unlock_irqrestore(&b->lock, flags);

---
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

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/21539340647

AI-authorship-score: low
AI-authorship-explanation: The commit has typical human characteristics: domain-specific BPF knowledge, concise explanations, and follows kernel conventions.
issues-found: 1
issue-severity-score: high
issue-severity-explanation: Hash bucket mismatch causes selems to be inserted into wrong bucket and never properly unlinked, leading to hash list corruption.