Suppose all the telephone companies and ISPs announce clearly the days/weeks/years when they *don't* get NSLs. Would they be breaking the terms of the NSLs then? Or do we know that they all get NSLs, and we just don't know how many, or more importantly, what they say.
Good point.
The boundary would be any structure member offset from 0, like in the example. Otherwise, it could
be the architectural page size (for x86 it'd be 4K).
But it doesn't need a boundary if checked at a stage where the original construct is still accessible.
if ptr->member is used before ptr is checked for NULL, throw
the warning. Most coding is not going to make a structure that starts at zero. I can imagine
doing it in 16-bit real mode code, maybe, but not sure it'd happen even then, and then the warning
could be disabled.
This would be useful, and in the kernel, most coders would be surprised by such an optimization
and would rather fix the problem or, as has been the case with some truly unnecessary checks,
remove them from the source.
I agree that gcc should make it a warning. It may be that it identifies it too late (in optimization)
and no longer has line number info?
I also agree this is due to a kernel bug, but a warning could've eliminated that.
Why do we still allow users to map stuff at page 0?
This compiler optimization is clever and useful, but it assumes that
0 is an invalid address (as it should be and usually is). The exploit
is taking advantage of the fact that mmap to address 0 is allowed.
To answer my own question: mmap to 0 might be useful
for emulation sometimes, for example, if emulating an IBM-PC BIOS
in 16-bit mode where physical memory 0 is valid. Also, it'd break
things to change it now. We could require a special system
setting before allowing users to do that, but that would also break
things.
However, there's hope for the NULL deref bugs in the kernel.
I've seen patches to fix such problems which seem to be identified
by static analysis tools, so someone's running them.
Very interesting exploit, though.
Point taken, but perhaps "view source" doesn't show you the original source.
It makes sense that they would strip comments before putting it on the server.
I
Well, lah-di-dah. I didn't choose the place of my birth, but I think I come from an OK place, too. And I have two engineering degrees, so there!:-)
I don't think the units had as much to do with it as the ambiguity of area vs. dimensional size. Since the original posting had said "measured 25 mm square" it wasn't clear whether it was referring to it's area or actual dimensions. Go have a pint of ale on me.
I agree that rights were violated here and the store doesn't have the right to inspect bags, and especially that people shouldn't be required to show ID without cause.
But, please also think about this: the store is trying to cut down on fraud and theft with any method they can, within reason. If the store were to give up on loss prevention, they'd be forced to raise prices. How much of every purchase you make are you willing to put towards subsidizing fraud and shoplifting by others? We already have high credit card interest and fees because of fraud losses, and the banks pass that cost on to us. Why not help them reduce costs if we can?
There's a delicate balance here, though, we need a way of helping to cut down on fraud without an erosion of our rights. Perhaps the present situation isn't so bad: most of us voluntarily comply with requests to inspect our purchases, and a few people protest to remind the stores that they can't force us to comply.
Joe
They seem to be thinking that the access points do
all the transmitting. Since laptops also transmit,
by their logic they would have to ban those, too, and nobody would get to use WiFi in the airport.
That can't be what they want.
Slashdot Mirror
Suppose all the telephone companies and ISPs announce clearly the days/weeks/years when they *don't* get NSLs. Would they be breaking the terms of the NSLs then? Or do we know that they all get NSLs, and we just don't know how many, or more importantly, what they say.
And Amazon is guaranteed to last forever and never change the terms of service.
But it doesn't need a boundary if checked at a stage where the original construct is still accessible. if ptr->member is used before ptr is checked for NULL, throw the warning. Most coding is not going to make a structure that starts at zero. I can imagine doing it in 16-bit real mode code, maybe, but not sure it'd happen even then, and then the warning could be disabled.
This would be useful, and in the kernel, most coders would be surprised by such an optimization and would rather fix the problem or, as has been the case with some truly unnecessary checks, remove them from the source.
I agree that gcc should make it a warning. It may be that it identifies it too late (in optimization) and no longer has line number info?
I also agree this is due to a kernel bug, but a warning could've eliminated that.
Why do we still allow users to map stuff at page 0? This compiler optimization is clever and useful, but it assumes that 0 is an invalid address (as it should be and usually is). The exploit is taking advantage of the fact that mmap to address 0 is allowed. To answer my own question: mmap to 0 might be useful for emulation sometimes, for example, if emulating an IBM-PC BIOS in 16-bit mode where physical memory 0 is valid. Also, it'd break things to change it now. We could require a special system setting before allowing users to do that, but that would also break things. However, there's hope for the NULL deref bugs in the kernel. I've seen patches to fix such problems which seem to be identified by static analysis tools, so someone's running them. Very interesting exploit, though.
Point taken, but perhaps "view source" doesn't show you the original source. It makes sense that they would strip comments before putting it on the server. I
Well, lah-di-dah. I didn't choose the place of my birth, but I think I come from an OK place, too. :-)
And I have two engineering degrees, so there!
I don't think the units had as much to do with it as the ambiguity of area vs. dimensional size.
Since the original posting had said "measured 25 mm square" it wasn't clear whether it
was referring to it's area or actual dimensions. Go have a pint of ale on me.
In the announcement, Intel says the area is 25 square mm,
which is a lot smaller than 25 mm square (25 mm on each side).
A nit, perhaps.
I agree that rights were violated here and the store doesn't have the right to inspect bags, and especially that people shouldn't be required to show ID without cause. But, please also think about this: the store is trying to cut down on fraud and theft with any method they can, within reason. If the store were to give up on loss prevention, they'd be forced to raise prices. How much of every purchase you make are you willing to put towards subsidizing fraud and shoplifting by others? We already have high credit card interest and fees because of fraud losses, and the banks pass that cost on to us. Why not help them reduce costs if we can? There's a delicate balance here, though, we need a way of helping to cut down on fraud without an erosion of our rights. Perhaps the present situation isn't so bad: most of us voluntarily comply with requests to inspect our purchases, and a few people protest to remind the stores that they can't force us to comply. Joe
They seem to be thinking that the access points do all the transmitting. Since laptops also transmit, by their logic they would have to ban those, too, and nobody would get to use WiFi in the airport. That can't be what they want.