netdev - Re: [PATCH bpf-next v2] libbpf: prevent overwriting of log_level in bpf_object__load

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Date:   Wed, 29 May 2019 19:37:55 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Quentin Monnet <quentin.monnet@...ronome.com>,
        Alexei Starovoitov <ast@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        oss-drivers@...ronome.com
Subject: Re: [PATCH bpf-next v2] libbpf: prevent overwriting of log_level in
 bpf_object__load_progs()

On 05/29/2019 04:26 PM, Quentin Monnet wrote:
> There are two functions in libbpf that support passing a log_level
> parameter for the verifier for loading programs:
> bpf_object__load_xattr() and bpf_prog_load_xattr(). Both accept an
> attribute object containing the log_level, and apply it to the programs
> to load.
> 
> It turns out that to effectively load the programs, the latter function
> eventually relies on the former. This was not taken into account when
> adding support for log_level in bpf_object__load_xattr(), and the
> log_level passed to bpf_prog_load_xattr() later gets overwritten with a
> zero value, thus disabling verifier logs for the program in all cases:
> 
> bpf_prog_load_xattr()             // prog->log_level = attr1->log_level;
> -> bpf_object__load()             // attr2->log_level = 0;
>    -> bpf_object__load_xattr()    // <pass prog and attr2>
>       -> bpf_object__load_progs() // prog->log_level = attr2->log_level;
> 
> Fix this by OR-ing the log_level in bpf_object__load_progs(), instead of
> overwriting it.
> 
> v2: Fix commit log description (confusion on function names in v1).
> 
> Fixes: 60276f984998 ("libbpf: add bpf_object__load_xattr() API function to pass log_level")
> Reported-by: Alexei Starovoitov <ast@...nel.org>
> Signed-off-by: Quentin Monnet <quentin.monnet@...ronome.com>

That's better, applied, thanks!