linux-kernel - Re: [PATCH v2 1/2] bpf: fix reuse of DEVMAP

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Message-ID: <77510736c4220e4f745fd152721e86689d8636d8.camel@gmail.com>
Date: Wed, 13 Aug 2025 14:59:50 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Yureka Lilian <yuka@...a.dev>, Andrii Nakryiko <andrii@...nel.org>, 
 Alexei Starovoitov	 <ast@...nel.org>, Daniel Borkmann
 <daniel@...earbox.net>, Martin KaFai Lau	 <martin.lau@...ux.dev>, Song Liu
 <song@...nel.org>, Yonghong Song	 <yonghong.song@...ux.dev>, John Fastabend
 <john.fastabend@...il.com>, KP Singh	 <kpsingh@...nel.org>, Stanislav
 Fomichev <sdf@...ichev.me>, Hao Luo	 <haoluo@...gle.com>, Jiri Olsa
 <jolsa@...nel.org>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] bpf: fix reuse of DEVMAP

On Wed, 2025-08-13 at 22:09 +0200, Yureka Lilian wrote:
> Previously, re-using pinned DEVMAP maps would always fail, because
> get_map_info on a DEVMAP always returns flags with BPF_F_RDONLY_PROG set,
> but BPF_F_RDONLY_PROG being set on a map during creation is invalid.
> 
> Thus, ignore the BPF_F_RDONLY_PROG flag on both sides when checking for
> compatibility with an existing DEVMAP.
> 
> Ignoring it on both sides ensures that it continues to work on older
> kernels which don't set BPF_F_RDONLY_PROG on get_map_info.
> 
> The same problem is handled in a third-party ebpf library:
> - https://github.com/cilium/ebpf/issues/925
> - https://github.com/cilium/ebpf/pull/930
> 
> Fixes: 0cdbb4b09a06 ("devmap: Allow map lookups from eBPF")
> Signed-off-by: Yureka Lilian <yuka@...a.dev>
> ---

Reviewed-by: Eduard Zingerman <eddyz87@...il.com>

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