Re: [PATCH 1/2] bpf: Fix incorrect handling of user flags by percpu map updates

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] bpf: bpf_percpu_array_update() misses validation for mutually exclusive flags
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commit 41d85d3576867a24ad9b52f72cd4c1d7b23504a6
Author: Masoud Aghasi <maghasi@disroot.org>

bpf: Fix incorrect handling of user flags by percpu map updates

This commit fixes incorrect handling of BPF_EXIST, BPF_NOEXIST, BPF_F_CPU,
and BPF_F_ALL_CPUS flag combinations in BPF_MAP_TYPE_PERCPU_HASH and
BPF_MAP_TYPE_PERCPU_ARRAY map updates.

> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index 0ce26b538075e..463f43b19e5cd 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
> @@ -438,7 +438,7 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
>  	u32 size;
>  	int cpu, off = 0;
>  
> -	if (unlikely((map_flags & BPF_F_LOCK) || (u32)map_flags > BPF_F_ALL_CPUS))
> +	if (unlikely((u32)map_flags & ~(BPF_EXIST | BPF_NOEXIST | BPF_F_CPU | BPF_F_ALL_CPUS)))
>  		/* unknown flags */
>  		return -EINVAL;
>  
> @@ -446,7 +446,7 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
>  		/* all elements were pre-allocated, cannot insert a new one */
>  		return -E2BIG;
>  
> -	if (unlikely(map_flags == BPF_NOEXIST))
> +	if (unlikely(map_flags & BPF_NOEXIST))

[Severity: Low]
Does this validation correctly handle the case where both BPF_EXIST and
BPF_NOEXIST are passed together?

Since the mask check above allows this mutually exclusive combination through,
evaluating `map_flags & BPF_NOEXIST` as true here will return -EEXIST instead
of the expected -EINVAL error code. Should an explicit check for the 
combination of BPF_EXIST and BPF_NOEXIST be added here, similar to the one
added for hash maps in htab_map_check_update_flags() in this same patch?

>  		/* all elements already exist */
>  		return -EEXIST;

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Sashiko AI review · https://sashiko.dev/#/patchset/20260928102821.995214-1-maghasi@disroot.org?part=1