Messages in this thread | | | Date | Tue, 6 Mar 2018 19:42:26 +0100 | From | Adam Borowski <> | Subject | Re: [PATCH 1/2] vsprintf: distinguish between (null), (err) and (invalid) pointer derefs |
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On Tue, Mar 06, 2018 at 09:22:17PM +0300, Alexey Dobriyan wrote: > > +#define BAD_PTR_STRING(x) (!(x) ? "(null)" : IS_ERR(x) ? "(err)" : "(invalid)") > > This is getting ridiculous. > > Instead of simply printing a pointer as %08lx or %016llx, not only glibc > (null) stupidity is propagated but expanded and "improved".
This is not about printing a pointer, this is about attempting to print an object referenced by such a bad pointer. Which leads to a crash: in userspace, you get a segfault; in the kernel, at least in the case I tested, the system is dead without even a squeal on either console or serial.
> I assure you reading 0000000000000000 is just as obvious as (null) and > reading fffffffffffffffa is just as good as -ENOMEM. > > In fact printing with hex is more information. Maybe it is important > that buggy pointer is small value but it's value is lost. > > Sure don't dereference a pointer for very small or very erry values > but print it without all the bell and whistles.
That's a reasonable suggestion, but it still needs to be special cased. Note the difference between printk("%px", 42) and printk("%s", 42).
See this part: - if (!ptr && *fmt != 'K' && *fmt != 'x') { + if (IS_BAD_PTR(ptr) && *fmt != 'K' && *fmt != 'x') { Printing the pointer is already excluded; what I'm fixing is: 1. lying that the bad pointer was (null) when it was -ENOMEM (commit 1) 2. crash when some bad code tries to printk("%s", -ENOMEM) (commit 2)
So, if what you propose is applying commit 2, and changing 1 to print the raw value instead of (null)/(err)/(invalid), that sounds good.
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