linux-kernel - Re: [PATCH bpf-next 1/2] bpf: Disallow BPF_F_LOCK with mixed special fields and centralize flag checks

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Message-Id: <df8fb7dc501dd081fcba56b592cba94e5aecd614ea4d3b595155dec551ecbca5@mail.kernel.org>
Date: Thu, 22 Jan 2026 16:02:11 +0000 (UTC)
From: bot+bpf-ci@...nel.org
To: leon.hwang@...ux.dev,bpf@...r.kernel.org
Cc: ast@...nel.org,daniel@...earbox.net,john.fastabend@...il.com,andrii@...nel.org,martin.lau@...ux.dev,eddyz87@...il.com,song@...nel.org,yonghong.song@...ux.dev,kpsingh@...nel.org,sdf@...ichev.me,haoluo@...gle.com,jolsa@...nel.org,shuah@...nel.org,leon.hwang@...ux.dev,linux-kernel@...r.kernel.org,linux-kselftest@...r.kernel.org,kernel-patches-bot@...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 1/2] bpf: Disallow BPF_F_LOCK with mixed special fields and centralize flag checks

> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 5936f8e2996f..c5863487ee73 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -3935,9 +3935,16 @@ static inline int bpf_map_check_op_flags(struct bpf_map *map, u64 flags, u64 all
>  	if ((u32)flags & ~allowed_flags)
>  		return -EINVAL;
>
> +	/* BPF_NOEXIST and BPF_EXIST are mutually exclusive. */
> +	if ((flags & (BPF_NOEXIST | BPF_EXIST)) == (BPF_NOEXIST | BPF_EXIST))
> +		return -EINVAL;
> +
>  	if ((flags & BPF_F_LOCK) && !btf_record_has_field(map->record, BPF_SPIN_LOCK))
>  		return -EINVAL;
>
> +	if ((flags & BPF_F_LOCK) && btf_record_has_field(map->record, ~BPF_SPIN_LOCK))
> +		return -EOPNOTSUPP;
> +
>  	if (!(flags & BPF_F_CPU) && flags >> 32)
>  		return -EINVAL;

[ ... ]

> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
> index e2fe6c32822b..80b50091cbbf 100644
> --- a/kernel/bpf/bpf_local_storage.c
> +++ b/kernel/bpf/bpf_local_storage.c
> @@ -493,13 +493,6 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
>  	unsigned long flags;
>  	int err;
>
> -	/* BPF_EXIST and BPF_NOEXIST cannot be both set */
> -	if (unlikely((map_flags & ~BPF_F_LOCK) > BPF_EXIST) ||
> -	    /* BPF_F_LOCK can only be used in a value with spin_lock */
> -	    unlikely((map_flags & BPF_F_LOCK) &&
> -		     !btf_record_has_field(smap->map.record, BPF_SPIN_LOCK)))
> -		return ERR_PTR(-EINVAL);
                ^^^^

This validation was removed from bpf_local_storage_update() but it appears
that no call to bpf_map_check_op_flags() was added in the local storage map
update functions. For array and hash maps, calls to bpf_map_check_op_flags()
were added in array_map_update_elem() and htab_map_update_elem(). However,
the local storage update functions like bpf_cgrp_storage_update_elem(),
bpf_fd_inode_storage_update_elem(), and bpf_fd_sk_storage_update_elem() pass
map_flags directly to bpf_local_storage_update() without calling
bpf_map_check_op_flags() first.

The syscall path does call bpf_map_check_op_flags() in map_update_elem() with
allowed_flags set to ~0, which catches the NOEXIST/EXIST mutual exclusion and
BPF_F_LOCK validation. But with allowed_flags=~0, the check for unknown flags
((u32)flags & ~allowed_flags) always passes zero, meaning unknown flags like
8 or 16 would not be rejected.

The old check (map_flags & ~BPF_F_LOCK) > BPF_EXIST rejected any unknown flag
bits. Is there a missing call to bpf_map_check_op_flags() in the local storage
update functions that should specify the allowed flags?

> -
>  	if (gfp_flags == GFP_KERNEL && (map_flags & ~BPF_F_LOCK) != BPF_NOEXIST)
>  		return ERR_PTR(-EINVAL);

[ ... ]


---
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See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/21254704407