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Message-ID: <537d82d4-9893-4329-874a-0a4f24af1a0d@lunn.ch>
Date: Tue, 7 Mar 2023 14:47:40 +0100
From: Andrew Lunn <andrew@...n.ch>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Sean Anderson <sean.anderson@...o.com>,
Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org,
"David S . Miller" <davem@...emloft.net>,
Vladimir Oltean <olteanv@...il.com>,
linux-kernel@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>,
Eric Dumazet <edumazet@...gle.com>,
Florian Fainelli <f.fainelli@...il.com>,
Tobias Waldekranz <tobias@...dekranz.com>,
Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net-next] net: mdio: Add netlink interface
On Mon, Mar 06, 2023 at 10:48:48PM +0000, Russell King (Oracle) wrote:
> On Mon, Mar 06, 2023 at 03:45:16PM -0500, Sean Anderson wrote:
> > +static int mdio_nl_eval(struct mdio_nl_xfer *xfer)
> > +{
> > + struct mdio_nl_insn *insn;
> > + unsigned long timeout;
> > + u16 regs[8] = { 0 };
> > + int pc, ret = 0;
>
> So "pc" is signed.
>
> > + int phy_id, reg, prtad, devad, val;
> > +
> > + timeout = jiffies + msecs_to_jiffies(xfer->timeout_ms);
> > +
> > + mutex_lock(&xfer->mdio->mdio_lock);
> > +
> > + for (insn = xfer->prog, pc = 0;
> > + pc < xfer->prog_len;
>
> xfer->prog_len is signed, so this is a signed comparison.
>
> > + case MDIO_NL_OP_JEQ:
> > + if (__arg_ri(insn->arg0, regs) ==
> > + __arg_ri(insn->arg1, regs))
> > + pc += (s16)__arg_i(insn->arg2);
>
> This adds a signed 16-bit integer to pc, which can make pc negative.
>
> And so the question becomes... what prevents pc becoming negative
> and then trying to use a negative number as an index?
I don't know ebpf very well, but would it of caught this? I know the
aim of this is to be simple, but due to its simplicity, we are loosing
out on all the inherent safety of eBPF. Is a eBPF interface all that
complex? I assume you just need to add some way to identify MDIO
busses and kfunc to perform a read on the bus?
Andrew
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