Messages in this thread | | | Date | Mon, 6 Mar 2023 22:48:48 +0000 | From | "Russell King (Oracle)" <> | Subject | Re: [PATCH net-next] net: mdio: Add netlink interface |
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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 think prog_len and pc should both be unsigned, then the test you have will be unsigned, and thus wrapping "pc" around zero makes it a very large integer which fails the test - preventing at least access outside of the array. Better still would be a validator that checks that the program is in fact safe to execute.
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