Re: [RFC patch] vsprintf: Allow %pe to print non PTR_ERR %pe uses as decimal
From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Date: 2021-03-24 22:37:35
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On 24/03/2021 23.18, Joe Perches wrote:
On Wed, 2021-03-24 at 22:27 +0100, Rasmus Villemoes wrote:quoted
On 24/03/2021 20.24, Joe Perches wrote:quoted
On Wed, 2021-03-24 at 18:33 +0100, Rasmus Villemoes wrote:quoted
On 24/03/2021 18.20, Joe Perches wrote:quoted
Maybe it's better to output non PTR_ERR %pe uses as decimal so this sort of code would work.No, because that would leak the pointer value when somebody has accidentally passed a real kernel pointer to %pe.I think it's not really an issue. _All_ code that uses %p<foo> extensions need inspection anyway.There are now a bunch of sanity checks in place that catch e.g. an ERR_PTR passed to an extension that would derefence the pointer; enforcing that only ERR_PTRs are passed to %pe (or falling back to %p) is another of those safeguards.quoted
It's already possible to intentionally 'leak' the ptr value by using %pe, -ptr so I think that's not really an issue.Huh, what? I assume -ptr is shorthand for (void*)-(unsigned long)ptr. How would that leak the value if ptr is an ordinary kernel pointer? That's not an ERR_PTR unless (unsigned long)ptr is < 4095 or so.You are confusing ERR_PTR with IS_ERR
No I'm not, I'm just being slightly sloppy - obviously when I say "not an ERR_PTR" I mean "not the result of ERR_PTR applied to a negative errno value", or "not the result of a valid invocation of ERR_PTR". But yes, feel free to read "not an ERR_PTR" as "something for which IS_ERR is false". Can you expand on why you think %pe, -ptr would leak the value of ptr?
quoted
If you want to print the pointer value just do %px. No need for silly games.There's no silly game here. %pe would either print a string or a value.
A hashed value, that is, never the raw value.
It already does that in 2 cases.
Yes, if you pass it ERR_PTR(-1234) (where no E symbol exists) or ERR_PTR(-EINVAL) but CONFIG_SYMBOLIC_ERRNAME=n, it prints the value in decimal, because people will probably recognize "-22" and values in that range don't reveal anything about the kernel image. Anything outside [-4095,0] or so is hashed. Rasmus _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel