linux-kernel - Re: [PATCH v3 1/2] bpf: Skip scalar adjustment for BPF

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Message-ID: <3b9a4aae9265fd8cc9a7c9576b8b1c54cd2933d1.camel@gmail.com>
Date: Wed, 01 Oct 2025 11:54:01 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Brahmajit Das <listout@...tout.xyz>
Cc: syzbot+d36d5ae81e1b0a53ef58@...kaller.appspotmail.com,
 andrii@...nel.org, 	ast@...nel.org, bpf@...r.kernel.org,
 daniel@...earbox.net, haoluo@...gle.com, 	john.fastabend@...il.com,
 jolsa@...nel.org, kpsingh@...nel.org, 	linux-kernel@...r.kernel.org,
 martin.lau@...ux.dev, sdf@...ichev.me, 	song@...nel.org,
 syzkaller-bugs@...glegroups.com, yonghong.song@...ux.dev, 
	kafai.wan@...ux.dev
Subject: Re: [PATCH v3 1/2] bpf: Skip scalar adjustment for BPF_NEG if dst
 is a pointer

On Thu, 2025-10-02 at 00:19 +0530, Brahmajit Das wrote:
> On 01.10.2025 11:29, Eduard Zingerman wrote:
> > On Wed, 2025-10-01 at 15:26 +0530, Brahmajit Das wrote:
> > > In check_alu_op(), the verifier currently calls check_reg_arg() and
> > > adjust_scalar_min_max_vals() unconditionally for BPF_NEG operations.
> > > However, if the destination register holds a pointer, these scalar
> > > adjustments are unnecessary and potentially incorrect.
> > > 
> > > This patch adds a check to skip the adjustment logic when the destination
> > > register contains a pointer.
> > > 
> > > Reported-by: syzbot+d36d5ae81e1b0a53ef58@...kaller.appspotmail.com
> > > Closes: https://syzkaller.appspot.com/bug?extid=d36d5ae81e1b0a53ef58
> > > Fixes: aced132599b3 ("bpf: Add range tracking for BPF_NEG")
> > > Suggested-by: KaFai Wan <kafai.wan@...ux.dev>
> > > Signed-off-by: Brahmajit Das <listout@...tout.xyz>
> > > ---
> > 
> > Acked-by: Eduard Zingerman <eddyz87@...il.com>
> > 
> Thanks
> > 
> > Nit: I'd made this a bit simpler: `regs[insn->dst_reg].type == SCALAR_VALUE`,
> >      instead of __is_pointer_value() call.
> > 
> > >  			err = check_reg_arg(env, insn->dst_reg, DST_OP_NO_MARK);
> > >  			err = err ?: adjust_scalar_min_max_vals(env, insn,
> > >  							 &regs[insn->dst_reg],
> Do I need to send a v4?

As you see fit.
If you agree with my suggestion, please send v4,
leaving it as-is also fine by me.