Re: [RFC PATCH bpf-next 1/5] bpf: fix potential error return

[Anton Protopopov <aspsk@isovalent.com>]

On Tue, Jan 30, 2024 at 12:20:06PM +0100, Jiri Olsa wrote:
> On Mon, Jan 22, 2024 at 04:49:32PM +0000, Anton Protopopov wrote:
> > The bpf_remove_insns() function returns WARN_ON_ONCE(error), where
> > error is a result of bpf_adj_branches(), and thus should be always 0
> > However, if for any reason it is not 0, then it will be converted to
> > boolean by WARN_ON_ONCE and returned to user space as 1, not an actual
> > error value. Fix this by returning the original err after the WARN check.
> > 
> > Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
> 
> nice catch
> 
> Acked-by: Jiri Olsa <jolsa@kernel.org>
> 
> > ---
> >  kernel/bpf/core.c | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> > index fbb1d95a9b44..9ba9e0ea9c45 100644
> > --- a/kernel/bpf/core.c
> > +++ b/kernel/bpf/core.c
> > @@ -532,6 +532,8 @@ struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
> >  
> >  int bpf_remove_insns(struct bpf_prog *prog, u32 off, u32 cnt)
> >  {
> > +	int err;
> > +
> >  	/* Branch offsets can't overflow when program is shrinking, no need
> >  	 * to call bpf_adj_branches(..., true) here
> >  	 */
> > @@ -539,7 +541,12 @@ int bpf_remove_insns(struct bpf_prog *prog, u32 off, u32 cnt)
> >  		sizeof(struct bpf_insn) * (prog->len - off - cnt));
> >  	prog->len -= cnt;
> >  
> > -	return WARN_ON_ONCE(bpf_adj_branches(prog, off, off + cnt, off, false));
> > +	err = bpf_adj_branches(prog, off, off + cnt, off, false);
> > +	WARN_ON_ONCE(err);
> > +	if (err)
> > +		return err;
> > +
> > +	return 0;
> 
> could be just 'return err'

Thanks.  I am inserting some code in a consequent patch in between,
so left this in this form

> jirka
> 
> >  }
> >  
> >  static void bpf_prog_kallsyms_del_subprogs(struct bpf_prog *fp)
> > -- 
> > 2.34.1
> >